Nonruminant Nutrition: Sow Feeding

Continuous milking (CM) of bST-supplemented primiparous cows results in production losses of 20 to 25%, suggesting mammary growth was inhibited. We hypothesized continuous (throughout late gestation and early lactation) bST supplementation and/or early-lactation increased milking frequency (IMF) would alleviate production losses in CM glands through improved mammary epithelial cell (MEC) functionality and proliferation. Primiparous cows were randomly assigned to either continuous bST (+bST; n = 4) or no bST (-bST; n = 4) treatment throughout the experiment. Within each animal, udder halves were randomly assigned to either CM or a 60-d dry period (CTL) treatment. CTL halves were dried -60 d relative to expected parturition date. CM glands were milked twice daily until parturition or spontaneous dry-off. At parturition all cows were milked four times daily (4X) until 30 d postpartum. Time points for mammary biopsies averaged -19, -7, +2, +7, and +20 d relative to parturition. Average d dry for CTL glands was 59.5 and 49.3 d for 4X+bST and 4X-bST treatments. Due to spontaneous dry-off, CM halves were dry for an average of 1.0 and 13.5 d for 4X+bST and 4X-bST treatments. Prepartum half-udder milk yield was greater (P < 0.01) in +bST cows than -bST cows (11.7 vs. 9.2 kg/d). Postpartum milk yield was reduced (P < 0.01) in CM udder halves regardless of bST treatment (15.0 vs. 25.0 kg/d; CM vs. CTL). Milk composition (fat, protein, SCC linear score) was not affected by CM or bST. MEC proliferation (Ki67 antigen index) was greater (P < 0.01) in CTL glands at d -7 (6.2 vs. 3.4%, CTL vs. CM), but was not affected at d -19, +2, +7, or +20. MEC proliferation was unaffected by bST. Decreased milk yield in CM halves was not overcome by bST in primiparous cows milked 4X. Further, MEC proliferation was reduced in CM halves near parturition (-7 d).