Feeding the dairy herd
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Feeding the dairy herd - nutrition
Dairy Cow Nutrition
Figure 6. Lactation cycle phases with corresponding changes in milk production, milk fat percentage, milk protein percentage, DM intake, and body weight.
Nutrient requirements vary with the stage of lactation and gestation. Figure 6 illustrates the shape and relationship of curves for milk production, fat percentage, protein percentage, DM intake, and body weight change during lactation. Five distinct feeding phases can be defined to attain optimum production, reproduction and health of dairy cows:
- Early lactation—0 to 70 days (peak milk production) after calving (postpartum).
- Peak DM intake—70 to 140 days (declining milk production) postpartum.
- Mid- and late lactation—140 to 305 days (declining milk production) postpartum.
- Dry period—60 to 14 days before the next lactation.
- Transition or close-up period—14 days before to parturition.
Phase 1. Early lactation—0 to 70 days postpartum. Milk production increases rapidly during this period, peaking at 6 to 8 weeks after calving. Feed intake does not keep pace with nutrient needs for milk production, especially for energy, and body tissue will be mobilized to meet energy requirements for milk production. Adjusting the cow to the milking ration is an important management practice during early lactation. Increasing grain about 1 pound per day after calving will increase nutrient intake while minimizing off-feed problems and acidosis. Excessive levels of grain (over 60 percent of the total DM) can cause acidosis and a low milk fat percentage. Fiber level in the total ration should not be less than 18 percent ADF, 28 percent NDF. Forage should provide at least 21 percentage units of NDF or about 75 percent of the total NDF in the ration. Physical form of the fiber is also important. Normal rumination and digestion will be maintained if greater than 20 percent of the forage is 2 inches in length or longer. Chopping (less than 3/8 inch theoretical length of chop—TLC), grinding, and/or pelleting all reduce physical form of fiber and its effectiveness to stimulate rumination.
Protein is a critical nutrient during early lactation. Meeting or exceeding crude protein requirements during this period helps stimulate feed intake and permits efficient use of mobilized body tissue for milk production. Rations may need to contain 19 percent or more crude protein to meet requirements during this period. The type of protein (degradable or undegradable) and amount of protein to be fed will depend on ration ingredients, method of feeding, and milk production potential of the cow. A good guideline for many dairy producers to follow is to feed 1 pound of soybean meal or equivalent commercial supplement per 10 pounds of milk starting at 50 pounds of milk. If urea is fed, it would be best fed with corn silage or as part of the grain mix. Maximum amount to feed is .2 pounds per cow when ration protein level is high.
Low peak production and ketosis problems occur when nutrient levels are not met. Low peak production translates into low lactation production. A loss of 1 pound in peak milk production equates to a 220-pound loss for the lactation. If grain intake is increased too rapidly or is too high, off-feed, acidosis, and displaced abomasum are possible.
To increase nutrient intake:
- Feed top quality forage.
- Make sure the diet contains adequate amounts of CP, DIP and UIP.
- Increase grain intake at a constant rate after calving.
- Consider adding fat (1 to 1.5 lb/cow/day) to diets.
- Allow constant access to feed.
- Minimize stress conditions.
Phase 2. Peak DM intake—second 10 weeks postpartum. Cows should be maintained at peak production as long as possible. Feed intake is near maximum and can supply nutrient needs. Cows should no longer be losing body weight, and are either maintaining weight or slightly gaining weight (figure 6).
Grain intake can reach but should not exceed 2.5 percent of the cow's body weight (1300-lb cow can consume up to 32 lb of DM from grain). Adding grains or feeds high in digestible fiber to the ration may be necessary to help maintain an optimal rumen environment when these high levels (55 to 60 percent of the ration DM) of grain are being fed. In general, rations should not contain more than 40 percent NFC. Forage quality should still be high with intakes of at least 1.5 percent of the cow's body weight (DM basis) to maintain rumen function and normal fat test.
Potential problems during this period include a rapid drop or decline in milk production, low fat test, silent heat (no observed heat), and ketosis.
To maximize nutrient intake:
- Feed forages and grain several times a day.
- Feed the highest quality feeds available.
- Limit urea to .2 pound per cow per day.
- Continue to minimize stress conditions.
Phase 3. Mid- to late lactation—140 to 305 days postpartum. This phase will be the easiest to manage. Milk production is declining, the cow is pregnant, and nutrient intake will easily meet or exceed requirements. Grain feeding should be at a level to meet milk production requirements and begin to replace body weight lost during early lactation. Lactating cows require less feed to replace a pound of body tissue than dry cows. Young cows should receive additional nutrients for growth (2-year-old, 20 percent more; 3-year-old, 10 percent more than maintenance). Consider NPN as a source of supplemental protein.
Potential problems during this phase are few. Milk production should slowly decline at an 8 to 10 percent drop per month. Avoid over-conditioning cows.
Summary—Phase 1, 2, and 3. Compare your current feeding program with the following guidelines:
- Protein: 18 to 19 percent CP (DM basis) in early lactation decreasing to 13 percent in late lactation. Undegradable or bypass protein (UIP) should be 35 to 40 percent of the CP in early lactation and 30 to 35 percent of CP in late lactation. About 30 percent of CP should be soluble protein (SIP).
- Net energy-lactation: .78 Mcal per pound of DM or greater in early lactation decreasing to .72 Mcal per pound in late lactation, and .6 Mcal per pound during the dry period.
- Forage amount: Minimum of 1.5 pounds of forage DM per 100 pounds of body weight. High quality legume forages should be the major source of forage fed during early lactation.
- Fiber: A minimum of 18 percent ADF in the dietary DM during early lactation increasing to 21 percent or greater in late lactation. Forages should provide a minimum of 21 percent NDF in the dietary DM.
- Nonfiber carbohydrates: 35 to 40 percent of the dietary DM.
- Fat: Maximum of 7 percent of the total ration DM with no more than 4 percent from supplemental fat. Limit fat from oilseeds to 2 percent of the ration DM.
- Salt: 0.5 percent of the ration DM or 1 percent of the grain mix.
- Mineral: Approximately 1 percent of the grain mix should be a calcium-phosphorus mineral.
- Urea: Maximum of .4 pounds of urea per day or 1 percent of the grain mix.
- Vitamins: Supplemented A, D, and E in rations to meet requirements.
- Ration form: Forages and grains should not be chopped or ground too fine.
Phase 4. Dry period—60 to 14 days before parturition. The dry period is a critical phase of the lactation cycle. A good, sound dry cow program can increase milk yield during the following lactation and minimize metabolic problems at or immediately following calving.
A dry cow feeding program separate from lactating cows is required. Diets should be formulated to specifically meet the nutrient requirements of dry cows: body maintenance, fetal growth, and replacing any additional body weight not replaced during phase 3. DM intake will be near 2 percent of the cow's body weight. Forage intake should be a minimum of 1 percent of body weight or 50 percent of the dietary DM. Grain feeding should be according to needs, but not exceeding 1 percent of body weight. One half of 1 percent of body weight in grain fed per day is usually sufficient in most dry cow feeding programs. Limiting the amount of feed DM offered to less than 2 percent of body weight may be necessary when rations contain only corn silage or other high energy feeds, to avoid over-conditioning of cows. Feeding low quality forages such as corn stalks or grass hay is preferable to limit feeding. If limit feeding is necessary, be sure ration is balanced to supply all nutrients in their correct amounts. A minimum of 12 percent CP in the DM is recommended.
Meet calcium and phosphorus needs, but avoid large excesses. Calcium intakes of 60 to 80 grams and phosphorus intakes of 30 to 40 grams are sufficient for most cows. Dry cow rations above .6 percent calcium and .4 percent phosphorus (DM basis) have substantially increased milk fever problems. Provide adequate amounts of vitamin A, D, and E in rations to improve calf survival and lower retained placenta and milk fever problems. Trace minerals, including selenium for most producers, should be adequately supplemented in dry cow diets.
Problems such as milk fever, displaced abomasum, retained placenta, fatty liver syndrome, fatty liver formation, and poor appetite, along with other metabolic disorders and diseases, are common in fat cows at freshening.
Key management factors include:
- Observe body condition of dry cows and adjust energy feeding as necessary.
- Meet nutrient requirements and avoid excessive feeding.
- Change to a transition ration starting 2 weeks before calving.
- Avoid excess calcium and phosphorus intakes.
- Limit salt to 1 ounce and limit other sodium-based minerals in the dry cow ration to reduce udder edema problems.
Phase 5. Transition period—14 days before to parturition. The transition or close-up dry cow feeding program is critical to adjusting dry cows and springing heifers to the lactation ration and preventing metabolic problems. Some grain, if not previously fed, should be fed starting two weeks before freshening. Introduction of grain is necessary to begin changing the rumen bacteria population over from an all-forage digestion population to a mixed population of forage and grain digesters. Also, addition of some ingredients used in the lactation ration during this period minimizes the stress of ration changes after calving. Some suggested management strategies during this period include:
- Provide 6 to 10 pounds of grain to adapt rumen microbes to fermentable carbohydrates and stimulate rumen papilla formation. The added grain sources, fed individually or as part of a lactating TMR, should be feeds that the fresh cow will be receiving.
- Increase protein in the ration to between 14 and 15 percent of the ration DM. Feeding some of this additional protein in the form of undegradable protein may be beneficial in supplying amino acids for fetal growth.
- Limit fat in the ration to .25 pounds. High fat feeding will depress DM intake.
- Maintain 6 to 10 pounds of long hay in the ration to stimulate rumination. If corn silage or a lactation TMR is fed, limit DM amounts to 1 percent of body weight.
- Remove salt from the ration if edema is a problem.
- If niacin (to control ketosis) and/or anionic salts (to help prevent milk fever) are going to be used, they should be included in the ration during this period.
Colostrum (either dam's colostrum or mixed colostrum from first milking of older cows) fed to calves as soon after birth as possible (ideally within 30 minutes and certainly within 4 hours) protects against disease. Early feeding of colostrum at 4 to 5 percent of birth weight is necessary because:
- Newborn calves have no antibodies to provide natural protection against disease until they receive colostrum.
- Calves' ability to absorb immunoglobulins (the disease protection component) is substantially reduced after 24–36 hours.
- Calves may become infected with highly pathogenic (disease-causing) bacteria immediately after birth.
- Colostrum is a concentrated source of ready available nutrients.
Within the first 24 hours after birth, calves should receive 12–15 percent of their birth weight as first-milking colostrum. Half of this should be within 4 to 6 hours after birth, and the remaining half 12 hours later. Hand feeding of colostrum through a nipple bottle or esophageal feeder is preferred to nursing, and assures that the calf receives the required amount of colostrum. Quality of colostrum can be determined by use of a colostrometer. Most calves require 200 to 300 grams of immunoglobulin to acquire passive immunity. Low quality, bloody or mastitic colostrum should not be fed.
Excess colostrum is a highly nutritious feed and can be fed after the calf has received the first milk colostrum during the first 24 hours of life. Undiluted excess colostrum contains about a third more solids than milk or reconstituted milk replacer, and is highly digestible. Storage and subsequent use of excess colostrum is highly desirable. It may be fed fresh; frozen or stored, then thawed prior to feeding; or stored as sour (fermented) colostrum.
Naturally fermented sour colostrum, stored in clean containers away from excessive heat, is an acceptable feed for calves more than 3 days old. Preservation of colostrum may also be achieved by adding propionic acid at 1 percent by weight (1 cup/6 gallons of colostrum).
Colostrum supplements. When colostrum is not available or quality is poor, commercial colostrum supplements may be useful. These contain bovine immunoglobulins and are prepared from cheese whey, colostrum from immunized cows, or monoclonial antibody technology. Efficacy may differ according to type of product and conditions of use. These preparations may be useful to enhance the antibody (IGg) content of low quality colostrum and increase low antibody titers in calves.
Comparing colostrum, transitional milk, milk and milk replacer. The composition of milk secretions changes rapidly after calving. First milk is considered true colostrum; secretions obtained for 4 to 5 days after the first milking are transitional milk. The first six milkings are higher in nutrients than normal milk or reconstituted milk replacers. In comparing milk replacers with a cow's natural secretions, take into account variations in both replacer quality and dilution rate. Table 6 shows a comparative analysis using a high quality milk replacer at standard dilution rates.
Milk replacers vary in quality. Study the feed tag. The best milk replacer contains 22 percent protein, all derived from milk products. The protein level should be 22 to 24 percent when chemically modified soy protein, soy isolates, or soy concentrates are used because plant proteins are less digestible than milk protein. Table 7 lists various sources of protein according to acceptability in milk replacers. Compare the protein sources listed on your milk replacer feed tag with this list.
The fat level in a good milk replacer powder should be at least 10 percent and may be over 20 percent. The higher fat level tends to reduce the severity of diarrhea and provides additional energy for growth. Good-quality animal fats are preferable to most vegetable fats. Soy lecithin, especially when homogenized, is another acceptable fat source and improves mixing properties of the replacer.
Carbohydrate sources that the calf can use include lactose (milk sugar) and dextrose. Two common carbohydrate sources that should be excluded from milk replacers are starch and sucrose (table sugar).
Mastitic milk or discard milk can be used as liquid feed for young calves. Discard milk is defined as unmarketable milk from cows that were treated with antibiotics. This milk can be fed fresh in the same manner as whole milk. Extremely abnormal milk (bloody or watery) should not be fed. Excess discard milk can be fermented or preserved chemically. Milk collected for three to six milkings after antibiotic treatment will ferment normally. Milk from the first milking after treatment does not ferment well alone, but usually ferments well when mixed with all unmarketable milk following treatment.
Properly managed feeding of mastitic milk to calves will not increase mortality or cause mastitis in these animals when they freshen. Calves fed pasteurized milk containing an added culture or live Staphylococcus aureus did not show evidence of the organism in body tissues 10 to 14 days after exposure. Also, at first lactation, heifers fed Staphylococcus aureus in pasteurized milk, as calves, did not have a greater incidence of infection than controls. Mastitic milk should not be fed to calves less than 2 days old, as the intestine is permeable to large protein molecules. Diarrhea is no more prevalent in calves fed mastitic milk than in calves fed whole milk. It is recommended that calves fed mastitic milk be housed separately to prevent suckling and introduction of organisms into the teat canal. Calves fed milk containing antibiotics should not be marketed for meat unless a suitable withdrawal period is used before slaughter. Although mastitic milk may be slightly higher in solids than whole milk, recommended feeding rates are similar.
Amount to feed, feeding frequency, and age of weaning. A prime consideration in raising the calf is to provide adequate DM for growth. DM from liquid feed should equal 1 percent of birth weight and should be fed from birth to weaning. For a 100–pound Holstein calf, 1 pound of DM daily could be provided from 8 pounds of milk, 6 pounds of surplus colostrum, 7 pounds of transitional milk, or 1.1 pounds of milk replacer plus 7 pounds of water. Estimate the DM percentage in the liquid diet and dilute as necessary in relation to the total volume offered the calf. Liquid feeds can be fed warm or cold, but using warm water will make mixing of replacer easier and may improve acceptability of replacer by calves.
Feeding milk or milk replacer by open pail is a common practice, although many calf raisers choose nipple feeding by pail or bottle. No real advantage in calf health or performance has been shown for either method. Automated feeding equipment can be used, but good management and observation are needed if the goal of weaning healthy calves is to be achieved. Always use and feed only from clean equipment.
Most calf raisers feed twice daily. For example, a 100-pound calf can be fed 4 pounds (2 quarts) of milk in the morning and 4 pounds of milk in the afternoon. Feeding twice daily assures at least two observations per day of the calf and probably is more satisfying to the calf. Weak or unthrifty calves may benefit from even more frequent feedings. Once-a-day feeding of milk-fed calves has proven successful except when calves are housed in the extreme cold or in otherwise undesirable environments. The keys to its success are keen observation to detect any sickness early and careful feeding of adequate nutrients without overfeeding. Calves fed once a day need the same amount of daily DM as twice-a-day fed calves, but liquid amounts may have to be reduced to avoid digestive upsets. Dry milk replacer can be added to whole or mastitic milk to increase solids content without increasing the volume of liquid fed. Although this procedure resulted in satisfactory gains and health, it has not been adopted as yet by many calf growers. If once-a-day feeding is practiced, calves should be observed at least once in addition to feeding time for general health and well-being.
Feeding programs for calves in hutches can be similar to those used for calves in nurseries during most of the year. During extremely cold weather, feeding rates should be increased because energy requirements of the calves will be greater. Increasing the amount fed by factors of 1.25 to 1.5 and offering the feed three times daily has helped provide the nutrients needed by these calves. Young calves that appear to be extremely cold and are doing poorly should be placed in warmer quarters.
Abrupt weaning of calves at an early age is an acceptable practice. Research has shown that calves may be weaned successfully at 3 weeks of age, but most producers wean between 4 and 8 weeks. Weaning later than 8 weeks could lead to fat calves. If they are weaned at 21 days, calves may have slightly depressed growth rates the first month after weaning. However, by 12 weeks of age, early-weaned and later-weaned calves (6 weeks) are of similar weights. Weaning according to starter intake (1 to 1-1/2 lb/day) is a good practice. Abrupt weaning usually stimulates dry feed consumption. Starter intake can be encouraged by placing the dry feed in the pail immediately after the liquid has been consumed. In general, early weaning can reduce feed and labor costs and good results can be obtained with weaning at 21 to 35 days. Calves doing poorly or calves eating less than 1 pound of starter per day should remain on a liquid feed until performance improves and dry feed is consumed in satisfactory amounts.
Preventing calf scours. Scours can develop as a result of several conditions. Avoid these if at all possible.
- Overcrowding–provide 24 to 28 square feet of bedded area or about 20 square feet of building floor space for calves raised in confined, elevated stalls.
- Inadequate ventilation–provide a minimum of 4 air exchanges per hour in winter, 15 in summer. Avoid direct drafts on the calf.
- Wet, damp calves–provide adequate bedding and good ventilation, and avoid spraying calves with water when cleaning facilities to help prevent calves from becoming chilled. Provide plenty of dry bedding in maternity stalls.
- Overfeeding–irregular amounts and too much of the wrong concentration or wrong kind of liquid diets are common causes of calf scours.
- Low resistance–vitamin A, D, and E supplementation (oral or injectable forms) immediately after birth is helpful in increasing the calf's natural resistance to scours, especially if colostrum is low in vitamin A content.
- No first–milk colostrum–don't assume the newborn calf has nursed. Many newborn calves don't receive enough colostrum to be protected from calfhood diseases. Feed colostrum, preferably by hand, as soon as possible after birth (minimum of 2 to 3 quarts to large breed calves; 3 pints to the smaller breed calves).
- Dirty utensils–clean the feeding utensils thoroughly after each feeding. Store upside down to drain all water out. Small amounts of excess wash water are perfect areas for bacteria to multiply rapidly.
Use of electrolytes. Early detection of sickness and prompt corrective action is important to prevent scours. When a calf has only a mild case of scours (not off-feed, not depressed, and no fever), feeding an oral electrolyte solution in addition to milk or milk replacer usually is beneficial. A suggested regimen is 4 feedings daily of 2 to 2.5 pints of milk or milk replacer, followed in 10 minutes by the same amount of an electrolyte solution. As the diarrhea begins to subside, the volume of electrolyte solution can be gradually decreased. Oral electrolyte solutions can be purchased commercially. If not readily available, an electrolyte mixture can be made by combining these kitchen cabinet ingredients:
|Mixture 1||Mixture 2|
1 package MCP pectin
1 teaspoon low-sodium salt
2 teaspoons baking soda
1 can beef consommé soup
Add water to make 2 quarts
4 teaspoons of table salt
3 teaspoons of baking soda
1/2 cup of "light" corn syrup
Add water to make 1 gallon
Starter rations. A good quality, palatable calf starter should be offered during the first week of life. The best calf starters are high in energy, free of excessive fines, and contain 18 percent CP (DM basis). To encourage intake, starters should consist of whole, coarsely ground, cracked, or rolled grains. Molasses (up to 5 percent of the mixture) improves palatability and minimizes fines and dust. Finely ground feeds become "pasty" and are undesirable. Whole grains, especially oats, can be fed with starter rations to calves up to 3 months of age. Calf starters should be fed until calves are about 12 weeks of age. Intake should be limited to 3 to 5 pounds per calf each day.
Many good commercial calf starters are available and convenient to feed. Simple, home-mixed calf starters may be equally acceptable. Table 8 gives examples of some good starter rations.
Additives. Coccidiostats and/or ionophores may be useful in reducing coccidiosis and in promoting growth. Some products (for coccidiosis) may be included in both milk replacers and starters. Ionophores can be used in starters to improve gain and feed efficiency. Other additives, such as direct–fed microbials and yeast products, have not been found to consistently improve growth rates.
Hay or silage for the young calf. While calves may begin nibbling on good quality hay as early as 5 to 10 days of age, it is not necessary to feed forages before 8 to 10 weeks of age. If forages are inconvenient because of the housing and management system, it may be desirable to incorporate a forage factor (more fiber) into the starter ration. Ration 3 (table 8) is an example of a suitable ration for calves not receiving hay or silage. Extremely high moisture silages and pastures should not be fed before 3 months of age because the high moisture content can limit intake and growth. Low moisture haylage is acceptable if it is kept fresh.
Water. Calves fed limited liquid (such as in a once-a-day feeding program) should receive supplemental water, especially during warm weather. Water can be offered free choice starting on day 4 of life. Make sure water is fresh and pails are cleaned daily. Calves offered water during the liquid feeding period (birth to 4 weeks) tend to consume more starter and perform better than calves just fed the liquid feed.
Summary of feeding program in early life. A carefully planned feeding program is necessary if calves are to thrive and grow. The feeding program can be summarized as follows:
|Day 1||Dam's colostrum|
|Day 2||Dam's colostrum|
|Day 3||Dam's colostrum|
|Day 4||Liquid feed of choice, introduce starter and water|
|Day 5 to weaning||Continue liquid feeding program|
|Weaning to 12 weeks||Starter (up to 5 lb daily), introduce forage if not previously fed|
If quality feeds are used and fed in satisfactory amounts under good conditions of management in the program described, replacement calves that are growthy, vigorous, and healthy should result.
For more information on calf nutrition and management, refer to North Central Regional Extension Publication #205, Raising Dairy Replacements.
Rearing the calf from 12 weeks to 1 year. During this period of the herd replacement's life, free-choice forage and limited grain can be fed. The amount of grain and protein content of the grain mix needed will be determined by the quality of forage(s) being fed. Pasture can be used successfully in the feeding program, but it should not be expected to supply all of the nutrients for calves in this age group. A grain mix and some stored forage are desirable for calves less than 6 months old on pasture. Table 9 illustrates the grain-concentrate needed for heifers with different forage qualities. If heifers cannot be grouped, a creep feeder is an option. Inclusion of low energy bulky feeds in the creep mix may be necessary to avoid excess energy intake with free choice feeding. Trace mineralized salt and a calcium-phosphorus supplement can be offered free-choice if not adequately supplied in the grain mix. All calves must have access to clean, fresh water.
During this stage of the feeding program, avoid overfeeding grain and allowing calves to become fat. Over–conditioned heifers produce less milk in later life than those reared on a more moderate level of nutrition. The key period in mammary gland development is between 3 and 9 months of age. During this period, mammary tissue is growing 3.5 times faster than body tissue. Heifers fed high-concentrate rations from calfhood to breeding age develop less milk secretory tissue in the mammary gland than heifers raised at normal, recommended growth rates. Fattening of heifers prior to puberty appears to have an inhibitory effect on mammary secretory tissue development and/or changes the endocrine stimulation of mammary gland growth. Accelerated growth rates for heifers 15 months of age and older does not affect mammary secretory tissue. Higher protein levels in the diet (14 to 16 percent) may help prevent over-conditioning when heifers are fed high-energy diets.
If protein content of forage is good, little protein supplement will be required in the grain mix. Grain mixes prepared for the milking herd are acceptable as long as they are properly fortified with minerals and vitamins. Monensin or Lasalocid (ionophores) can be fed in rations for heifers to improve rate of gain (table 17).
Feeding program for heifers 1 to 2 years of age (to 2 months before parturition). If good quality forage is available, this may be the only feed required for heifers over 1 year of age. Trace mineral salt and a calcium-phosphorus supplement are recommended on a free-choice basis. Heifers should gain 1.7 to 2.0 pounds per day. If growth is not satisfactory, some grain should be supplied; generally, only a small amount is required. Heifers on good pasture require no grain or additional forage. As pastures mature, dry out, or are heavily grazed, supplemental grain or other feed should be provided. Heifers deficient in energy, phosphorus, or vitamin A will not exhibit estrus.
First estrus in heifers is dependent on a combination of size and weight, but primarily weight. A general guideline is heifers will show their first estrus at 40 percent of their mature weight, which should be before 12 months of age. Heifers fed high planes of nutrition will show estrus at an earlier age than heifers grown at recommended rates, but underfeeding of heifers will delay estrus. Underfed or very slow growing heifers may ovulate, but estrus signs often are suppressed. Heifers in good condition and gaining weight at breeding time generally show more definite signs of estrus and have improved conception rates over heifers in poor condition and/or losing weight. Over-conditioned or fat heifers have been reported to require more services per conception than heifers of normal size and weight. Table 10 shows desirable weights for first breeding, together with weights for other age categories.
Two months before calving to calving. How heifers are fed during this period can affect milk production during first lactation. Heifers should move from a steady growth rate after breeding to a rapidly growing phase (1.7 to 2.0 lb/day gain) the last two to three months of pregnancy. Heifers growing rapidly at calving time, but needing additional growth during the first lactation, were found to be more persistent milkers than full-sized heifers at calving. Also, heifers slightly undersized at calving (80 percent of normal) will reach full milk production potential and normal size if fed sufficient nutrients for both growth and milk production during the lactation.
The exact amount of grain to feed before calving will depend on forage quality, size, and condition of the heifer. A thumb rule would be to feed grain at 1 percent of body weight starting about 6 weeks before calving. Be sure rations are balanced in protein, minerals, and vitamins. Excess salt intakes can contribute to udder edema and should be avoided the last 2 weeks before calving.
Well-grown heifers will have a minimum of problems at calving, but ease of calving can be affected by plane of nutrition in two ways: 1) an effect on calf size, and 2) an effect on fatness of the dam. At equal body weights, fat, over-conditioned heifers are almost always younger and consequently will have less skeletal growth than leaner, normally grown heifers. Thus, fat heifers have higher rates of dystocia because of small pelvic openings and usually a larger-than-normal sized calf at birth. Underfed or poorly grown heifers also will require more assistance at calving and have a higher death rate at calving than normal sized heifers.
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