Effect of forage quality on heifer growth
Nutrient requirements of post-weaned heifers can be determined based on the weight and age of the animal, environmental conditions, target age at first calving and expected mature weight. Feeding heifers in excess or below their actual requirements is not desirable as this can negatively impact future reproductive and lactation performance. If you are struggling with over- or under-conditioned heifers, one nutritional factor you may want to consider is forage quality.
Forage quality can significantly impact heifer growth; especially when heifers are limit fed grain and provided hay free choice. Recently, the University of Minnesota Southern Research and Outreach Center's Calf and Heifer Research Facility conducted a study to look at the impact of forage quality on Holstein dairy heifer growth from 3 to 6 months of age (112 days). Three alfalfa hay treatments were fed: low quality (108 RFV), medium quality (130 RFV), or high quality (155 RFV) hay. The crude protein concentration of the hays was very similar (within 1 percentage unit), averaging 19.1% across all hays. In contrast, the neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentration increased as forage quality decreased averaging 39.7%, 44.7% and 55.1% NDF, and 29.8%, 33.5% and 38.2% ADF for the high, low and medium quality hay, respectively. Heifers were limit fed a 16% crude protein grain mix at 6.0 lb/head/day (as-fed) for the first 14 days on trial and then were fed 4.0 lb/head/day (as-fed) for the remainder of the trial. Hay was offered free-choice. Animals were housed in groups with 6 heifers per pen and 4 pens per treatment. Results are shown in Table 1. They found grain intake was similar for all treatments with heifers consuming all offered grain through 112 d. However, heifers that were fed the medium quality hay consumed 0.5 lb more hay DM per day than heifers fed the low or high quality hay. They also reported that hay quality had a significant impact on body weight gain and stature growth. Heifers receiving the medium and high quality hay gained approximately 0.2 lb more per day and grew 0.7 more inches in height over the entire trial than heifers fed the low quality hay. In addition, heifers fed the high quality hay utilized feed 6.0% more efficiently than heifers fed the medium quality hay and 10.4% more efficiently than heifers fed the low quality hay.
If forage quality is negatively impacting heifer growth rates, what can you do?
To prevent excessive weight gain from high quality forages, one option is to limit feed forages. In general, heifers like high quality forages; therefore, they will consume more and gain more weight. Another option may be to decrease the energy concentration of the grain mix, for example, by adding higher fiber ingredients such as by-product feeds. If heifers will not consume enough low-quality forages to meet their nutrient requirements, blending the low quality forage with higher quality forage may be necessary.
What about economics?
As feed is the largest cost associated with raising a heifer, when choosing forage quality, economics should also be considered. In particular, it is useful to assess the trade-off between heifers' performance and forage cost. As shown in the Minnesota study, in which heifers gained 1.9 lb/d on the lowest quality hay, feeding lower quality forage and limit feeding grain can result in acceptable growth rates. Remember, however, that low quality forages must be palatable.