Effects of early lactation dietary starch amount on first calf heifer performance and health: A pilot study
It is clear that the first calf heifer is becoming an even more important and influential cow in the herd. In the past few years, the use of sexed semen has increased the number of first calf heifers entering the herd thus placing an emphasis on the importance of their success during the transition period. Recently, cull cow prices have resulted in favorable economic trends towards replacing older cows with first calf heifers. Also, due to the rising numbers of replacement heifers, overcrowding begins to become a concern in the fresh cow pen as well as the lactating herd.
Given the recent interest in dietary starch for fresh cows, combined with the influx of heifers into dairy herds, our dairy nutrition research group's most recent project was to determine the effects of varying dietary starch amount on performance and health of first calf heifers.
Evaluating dietary starch for dairy cattle is not a simple concept. Factors such as corn processing, storage method, particle size, dry matter intake, corn genetics and associative effects of ingredients in the diet impact starch digestion. Excessive rumen starch fermentation can decrease fiber digestibility and efficiency of microbial protein production, and reduce milk fat yield. According to Mike Allen, Michigan State University, high producing cows in early to mid-lactation typically perform well on high-starch diets; however, due to potential intake suppressing effects of high starch diets, they may not be ideal for fresh cows. Allen suggests that highly fermentable starch sources (such as high moisture corn) should be limited in diets for the first two weeks following parturition to avoid further depression in feed intake, and decrease risk of ruminal acidosis.
Concentration and ruminal digestibility of starch in diets of lactating cows has important effects on productivity and health. Fresh cow diets must supply sufficient amounts of energy to prevent excessive amounts of body fat mobilization, maintain rumen health and ensure adequate dry matter intake. Corn starch is a digestible source of energy that stimulates fiber digestion by rumen microbes. Ruminal fermentation of starch results in the microbial production of propionate, which the liver converts to glucose. The cow then uses glucose to make milk lactose. Although propionate is important to maintain high amounts of milk production, excessive amounts of propionate may actually reduce feed intake. Additionally, excessive amounts of rumen fermentation can result in acidosis. Acidosis reduces feed intake and may compromise immune function leading to an increased incidence and severity of immune-related disorders such as metritis and mastitis. Perhaps these effects are amplified in fresh cows.
We conducted a study in the fall of 2011 to evaluate the effects of varying pre- and postpartum dietary starch. As part of a larger study, we assigned 30 springing heifers to either a moderate starch diet (14.5%) or a high starch diet (17.9%) 42 days before expected calving. After calving, the heifers switched to their respective lactation diet of moderate starch (24.0%) or high starch (31.5%). The starch source for this trial was supplied by coarsely ground dry corn (Table 1 shows the lactation diet formulation). We do not advocate feeding high amounts of starch but fed elevated amounts of starch so that treatment differences could be realized.
The heifers were monitored for 56 days after calving recording daily dry matter intake, daily milk yield and weekly body weight, and observing feeding behavior on day 21 for a continuous 24-hour period with 10-minute scans.
The results from this study indicate that there was no difference in postpartum dry matter intake between the low and high starch treatments (Table 2). Heifers that received the high starch diet did lose slightly more body weight in the first 21 days but also had increased milk production as well as 3.5% fat corrected milk production compared to the low starch diet. Milk fat to protein ratio for this study was low indicating that heifers were not mobilizing excessive amounts of body fat (a fat to protein ratio >1.4 indicates fresh cows are at increased risk for ketosis). Feeding a higher amount of starch did increase the percentage of heifers with fat to protein ratio >1.4 compared with moderate starch fed heifers. Feeding and ruminating time was similar between treatments. Heifers fed low starch had both a lower incidence of metritis and lower percentage of milk samples with somatic cell count >400,000 SCC/mL within the first 21 days after calving. It is plausible that diet affected immune function although the mechanism for these effects remains unclear.
Future research should evaluate the effects of source and amount of starch fed to heifers and cows in early lactation to better understand the effect of starch on feed intake, health and reproductive efficiency. Greater milk production by heifers fed high starch is intriguing but the reduction of heifer health is a concern.
Other research efforts in the Upper Midwest are also shedding light on understanding of starch fermentation. Researchers at the University of Wisconsin have developed a spreadsheet to evaluate dry and high moisture corn on an equivalent basis using mean particle size and ammonia production. Additionally, Dairyland Labs, in cooperation with workers in Canada, have the capacity to determine the effects of starch source on fermentation kinetics, production of volatile fatty acids and microbial protein.
Table 1. Postpartum dietary ingredients and amounts fed to heifers to determine the effects of dietary starch amount on postpartum performance and health.
|Ingredient||Moderate starch (24%)||High starch (31.5%)|
|-------- % dry matter --------|
|Lactation protein mix||19.4||21.4|
|Coarsely ground corn||9.2||22.4|
|Liquid feed supplement||4.0||3.5|
Table 2. Preliminary results for heifers 21 days after calving to determine the effects of dietary starch amount on postpartum performance and health.
|Item||Moderate starch||High starch|
|DMI, % of body weight||3.4||3.3|
|Body weight change1, lb/21 d||-45.3||-58.5|
|Milk fat, %||3.5||3.7|
|3.5% fat corrected milk, lb/d||55.4||61.0|
|Cows > 1.4 fat:protein ratio2, %||7.1||25.0|
|Cows > 400,000 SCC/mL||21.4||50.0|
|Feeding time, hours/day||3.2||3.1|
|Ruminating time, hours/day||7.8||8.3|
1 Change in body weight from week 1 to week 3 postpartum.
2 A milk fat:protein ratio greater than (>) 1.4 indicates fresh cows are at increased risk for ketosis.
3 Metritis was defined by having a temperature above 103°F with white or excessive dark uterine discharge accompanied by foul odor.
Published in Dairy Star June 9, 2012