Influence of Post Calving Supplemental Protein on Calf Performance and Reproductive Efficiency for Beef Cows Fed Silage

 Research with dairy cows has shown that supplementation with protein of low to moderate degradability can increase milk yield, especially when the ration is silage based. Inadequate protein supply, either pre- or postpartum, can depress reproductive performance. With dairy cows, excessive crude and soluble protein in the diet can also depress reproductive performance. Since beef cows are fed diets with relatively low CP, problems of high CP influencing reproduction should be rare. However, beef cows fed good quality legume silage may be ingesting large amounts of highly soluble CP.

In trial 1, cows were placed on one of five feeding treatments: 0, 200, 400, 600 or 800 grams per day of corn gluten meal (CGM). Hay silage (13.7% CP, 62% TDN) was fed ad libitum. The treatment period was from calving (Jan 11 to March 12) to pasture turnout (May 25). Performance was monitored until calves were weaned on October 3. There was no effect of treatment on DMI, pasture cow weight loss or BCS changes. Calves from cows fed 400 g CGM/day were 36 and 44 kg heavier at weaning than calves from cows fed 0 or 800 g/day CGM, respectively. Overall rates of estrus detection, first service conception and calving interval were not influenced by protein supplementation. The percentage of cows pregnant was highest for cows fed 400 and 600 g CGM per day.

In the second trial cows were fed silage either ad lib or restricted (75% ad lib) and supplemented with 400 g/day CGM, 475g/day SBM or no supplement (control). Restricting the cow’s silage intake did not affect calf performance. Protein supplementation increased gains during supplementation and on pasture. There was a strong interaction between protein supplementation and level of silage feeding. When silage was fed ad lib, SBM was more effective than CGM for increasing calf gain. However, when silage was restricted, CGM was more effective. For cows fed ad lib, protein supplementation improved the percentage of cows pregnant and increased mobilization of body reserves. When energy intake was restricted, protein supplementation reduced the percentage of cows pregnant.

On silage-based diets, beef cows respond to supplemental protein in the diet by producing more milk. This can be attributed to the low efficiency with which silage protein is utilized in the rumen. When silage is fed ad lib, the response to supplemental protein may be due primarily to the increased protein supply, both degradable and undegradable. When silage (and hence energy) intake is restricted, the response may be attributed more to increased supply of undegradable protein. In cows fed silage ad lib, energy for increased milk production comes primarily from the diet. However, when silage and energy intake are restricted, cows in good condition draw on body energy reserves to sustain higher levels of milk production in response to protein supplementation. While the positive effect of supplemental protein on milk production may enhance breeding success when cows are in good condition, it can have the opposite effect when they are not.

Reference: Charmley et al. 1999. Can. J. Anim. Sci. 79:97.
Nutrition Update
Volume 10 No.3, February 2000