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How To Strategically Supplement Young Cows For Reproduction

Maintaining a yearly calving interval is imperative for a beef cow to remain a profitable calf producer in the herd, and can be a demanding task for young range beef cows.

Even with supplementation, young cows experience a period of negative energy balance and weight loss before and after calving, and their response to supplementation may vary from year to year. Poor reproductive performance of first-and second-calf cows is a challenge faced by cow-calf producers in the West.

 
Poorer-than-expected cow response to supplementation may be partially due to low availability of glucose (blood sugar) and impaired absorption of available glucose into tissues.

Cows absorb little glucose from their diet and rely on their body to produce glucose from other precursors.

If precursors are absent or in limited supply, glucose availability and absorption may be impaired, which might result in a shift in nutrient partitioning toward milk production at the expense of body weight gain and return to cyclicity.

Increasing the supply of glucose precursors in the diet may shift nutrients back toward postpartum weight gain and reproduction.

Propionate, a volatile fatty acid, is a primary precursor for glucose production. We investigated responses of 2-and 3-year-old postpartum cows to different amounts of propionate salt added to range protein supplements.

Experimental approach

Supplements were fed twice weekly at a rate of 2.5 lb per day for 70 days postpartum. Supplemental crude protein (CP) was approximately 50 percent ruminally degraded protein (RDP; degraded mostly in the rumen) and 50 percent ruminally undegraded protein (RUP; passes through the rumen relatively undegraded) and were fortified with minerals and vitamin A.

All supplements (30 percent CP) were based on wheat middlings, cottonseed meal, and feather meal, with increasing proportions (0, 80, or 160 g/d) of propionate salt (NutroCAL, Kemin Industries, Inc., abbreviated as RUP0, RUP80, and RUP160).

Outcomes and implications: What does this mean?

A supplement by year interaction was observed for days to first estrus. Cows fed RUP0 and RUP160 took longer to return to estrus in one year than the previous year, while cows fed RUP80 returned to cyclicity in similar days postpartum regardless of year.

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