# 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

## TL;DR

Feeding beef heifers at a moderate rate during early pregnancy increases milk protein concentration, but vitamin and mineral supplements during pregnancy do not affect milk yield or composition.

## Contribution

This study shows that early pregnancy nutrition affects milk protein concentration, but vitamin/mineral supplementation during pregnancy does not impact milk production or composition.

## Key findings

- Moderate body weight gain during early pregnancy increased milk protein concentration compared to low gain.
- Vitamin and mineral supplementation during pregnancy had no effect on milk yield or composition.
- Milk fat content increased after oxytocin administration and extended lag time in sample collection.

## 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.

Feeding first parity beef females at a moderate rate of gain during early pregnancy enhanced milk protein concentration. No differences were observed in milk yield and composition as a result of supplementation with vitamins and minerals throughout pregnancy.