Milking Frequency, Estradiol Cypionate, and Somatotropin Influence Lactation and Reproduction in Dairy Cows¹

Experimental protocol used in lactating Holstein cows between September 2000 and October 2001. Cows were milked either 2×or 4× daily during the first 30 DIM and then milked 2× thereafter. Cows also received either 10mg of estradiol cypionate (ECP) in oil or cottonseed oil between d 2 and 15 (8±2.6 d). In addition, cows received either bST (500mg of Posilac, Monsanto Co., St. Louis, MO) every 14 d starting at approximately 60 DIM, or did not receive bST (no bST). Ovulation was synchronized before AI by using the Heatsynch protocol starting 56 to 75 DIM. Blood was collected (B) before each injection (GnRH, PGF_2α, and ECP) during ovulation synchronization to determine cycling status before the onset of the Heat-synch protocol. In the first 82 of 144 cows studied, blood also was collected twice weekly during the first 60 DIM to determine ovulatory patterns. During the first 90 DIM, milk yields were recorded daily, and milk was collected once weekly to determine milk components (fat, protein, lactose, SNF, SCC, and MUN). TAI=timed AI.

Percentage changes in BCS relative to that assessed during the first week postpartum until approximately 9 wk of lactation. Cows were milked either 2× or 4× daily during the first 30 DIM, then 2× thereafter and injected with 10mg of ECP or cottonseed oil between d 2 and 15 postpartum (8±3 d). Body condition scores (±SE) during the first week postpartum for each treatment combination were: 2× Oil=2.7±0.08 (n=35); 2× ECP=2.7±0.08 (n=35); 4× Oil=2.9±0.08 (n=35); and 4× ECP=2.7±0.07 (n=37).

Percentage changes in BW relative to that assessed during the first week postpartum until about 9 wk of lactation. Cows were milked either 2× or 4× daily during the first 30 DIM, then 2× thereafter and injected with 10mg of ECP or cottonseed oil between d 2 and 15 postpartum (8±3 d). Body weights (±SE) during the first week postpartum for each treatment combination were: 2× Oil=603±18 (n=35); 2× ECP=605±18 (n=35); 4× Oil=612±18 (n=35); and 4× ECP=604±17 (n=37).

Percentage changes in daily milk yields were analyzed for the first 10 d after estradiol cypionate (ECP) injection. Cows were either milked 2× or 4× daily during the first 30 DIM, then 2× thereafter and injected with 10mg of ECP or cottonseed oil between d 2 and 15 postpartum (8±3 d). Milk weights (±SE) on d 0 (day of ECP or oil injection) for each treatment combination were: 2× Oil=26.9±1.5kg (n=36); 2× ECP=27.5±1.8kg (n=35); 4× Oil=29.2±1.4kg (n=36); and 4× ECP=32.3±1.9kg (n=40).