Effects of two different rates of body weight gain during the first trimester of pregnancy or supplementing vitamins and minerals throughout pregnancy on primiparous beef cow milk production and composition.

Abstract

We evaluated the effects of nutrition during pregnancy in beef heifers on colostrum and milk production and composition. For Experiment 1, crossbred Angus heifers were randomly allocated to a low (0.28 kg/d, [LG], n = 23) or a moderate rate of body weight gain (0.79 kg/d, [MG], n = 22) for 84 d after breeding, followed by management on a common diet until parturition. Colostrum samples were collected before first suckling and milk samples were collected by manual stripping of the teats 5 to 6 hours after calf removal on d 62 ± 10 and 103 ± 10 postpartum. At d 103, sampling techniques were compared by collecting a second sample after oxytocin administration and 90 s lag time. Colostrum somatic cell count was greater (P = 0.05) in LG (6,949 ± 797 × 10³ cells/mL) than MG (4,776 ± 797 × 10³ cells/mL) cows. In milk, percent protein was greater (P ≤ 0.01) in MG (3.03 ± 0.05%) than LG (2.87 ± 0.05%) cows. At d 103, oxytocin administration and extended lag time after teat stimulation increased milk fat content (P < 0.01) compared with immediate milk sample collection. For Experiments 2 and 3, crossbred Angus heifers were randomly assigned to receive either 113 g•heifer^-1•d^-1 of a vitamin and mineral supplement (VTM,) or no supplement (CON) from breeding until parturition. For Exp. 2, CON (n = 12) and VTM (n = 17) heifers were managed on a single pasture after parturition. On d 56 of lactation, 24-h milk production and composition were determined via a modified weigh-suckle-weigh technique using a portable milker. Milk yield and components (P ≤ 0.91) were similar between treatments. For Exp. 3, twice daily milk yield was recorded for 6 CON and 6 VTM heifers for 78 d following parturition. Milk samples were collected on d 32, 58, and 78 of lactation for component analysis. No differences were observed among treatments in milk yield or composition (P ≥ 0.09). Milk production was affected by day, increasing until d 10 and remaining similar (P ≥ 0.27) thereafter; however, protein was greater (P < 0.01) on d 58 compared with d 32 and d 78, and urea was reduced (P < 0.01) on d 78 compared with d 32 and 58. These experiments indicate that nutrition during early pregnancy has a sustained impact on milk protein but no impacts of vitamin/mineral nutrition during pregnancy were observed ion the subsequent lactation.