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Using corn co-products in post-partum diets of beef cows to optimize reproductive performance
Primiparous and multiparous Angus-Simmental cows (n = 48; BW = 537 kg ± 42.5; BCS = 5 ± .41) were used in a complete randomized block design to evaluate the effects of feeding DDGS as a primary source of dietary energy, which resulted in varying levels of protein during early lactation on; cow body weight, body condition, and reproductive performance. All cows were placed on study within 20 days of calving. Cows were blocked by calf birth weight, cow weight, BCS, and age and randomly assigned to one of three treatments: 1) silage-based total mixed ration (TMR; CON); 2) TMR with 2.5 kg/d DM DDGS (MID); or 3) TMR with 4.9 kg/d DM DDGS (HIGH). All diets were formulated to be isocaloric and either meet, or exceed all other nutrient requirements (NRC, 2000). Postpartum average daily gain (ADG) was targeted at .22 kg/d. Blood samples were collected at 7d intervals from trial initiation until estrous synchronization for determination of plasma progesterone concentration as an indicator of resumption of cyclicity. Blood samples were also collected at 21d intervals from trial initiation until estrous synchronization for plasma urea nitrogen (PUN). A 5-day Co-Synch + CIDR protocol was used and cows were bred by timed artificial insemination (TAI). Diameter of the largest antral follicle was determined at TAI via ultrasonography. Bulls were placed with cows 10d after TAI for the remainder of the breeding season. Pregnancy diagnosis was accomplished via ultrasonography 39 and 104d post-TAI, respectively, for TAI and overall breeding season pregnancy. Data were analyzed using the GLIMMIX, MIXED and GLM procedures of SAS. Final BW (P ≥ 0.44) and BCS (P ≥ 0.42) were similar among treatments. Neither resumption of cyclicity in cows (P = 1), dominate follicle diameter (P = 0.37), nor season long pregnancy rate (P = 0.99) were different between treatments. No difference (P = 0.72) in TAI conception rates were seen between cows fed MID (56.3%) and CON (62.5%) treatments. However, TAI conception rate in the HIGH cows (87.5%, P = 0.068), was higher and approached significance compared to CON and MID cows. Differences in PUN concentration were observe between all treatments (P≤ 0.002) with HIGH being the highest, MID intermediate and CON lowest. In summary, feeding high levels of DDGS to beef cows during early lactation has a positive effect on TAI conception rate which can potentially enhance cow herd genetic progress and producer profitability.
Keywords: Beef, Lactational programing, Heifer development