Oversupplying metabolizable protein in late gestation for beef cattle: Effects on prepartum BW, ruminal fermentation, nitrogen balance, and skeletal muscle catabolism

Citation

Hare, K.S., Wood, K.M., Acton, K., Fitzsimmons, C., Penner, G.B. (2019). Oversupplying metabolizable protein in late gestation for beef cattle: Effects on prepartum BW, ruminal fermentation, nitrogen balance, and skeletal muscle catabolism. Journal of Animal Science, [online] 97(1), 407-423. http://dx.doi.org/10.1093/jas/sky410

Plain language summary

The objective of this study was to determine the effect of oversupplying metabolizable protein on maternal body weight, nitrogen balance, digestibility, and abundance of catabolic proteins in pregnant beef cows during late gestation. Heifers were individually fed either a control treatment designed to meet protein requirements (CON) or a treatment providing 133% of protein requirements (HMP) for about 55 days before giving birth. Heifers fed HMP increased body weight by a greater magnitude than CON heifers 8 days before giving birth relative to 55 and 41 days before giving birth. Multiple measures of nitrogen balance were different between HMP and CON heifers. Heifers fed HMP had indicators of improved digestibility relative to CON heifers. The abundance of proteins involved in skeletal muscle catabolism was greater or tended to be greater for CON cows compared to HMP. Feeding greater quantities of metabolizable protein during late gestation may improve nitrogen balance, digestibility, and improve body weight gain prior to giving birth.

Abstract

The objective of the study was to determine the effect of oversupplying MP during late gestation on maternal BW, ruminal fermentation, nitrogen balance, and skeletal muscle catabolism. Crossbred Hereford heifers (n = 24) were assigned to a control treatment designed to meet MP requirements (CON) or a treatment providing 133% of the MP requirement (HMP). Heifers were individually fed their treatment from day-55 ± 3 relative to parturition and DMI was summarized by week. BW was measured on day-55 ± 3,-41 ± 3,-27 ± 3, and-8 ± 3. Ruminal digesta samples were collected on day-34 ± 5 and-15 ± 4 for short-chain fatty acid and ammonia-N (NH 3-N) concentration. Plasma was collected the day prior to ruminal digesta samples and analyzed for plasma urea-N. Nitrogen balance was measured over a 6-d period starting on day-34 ± 4 and-15 ± 4. Following completion of the N balance periods, muscle biopsies were collected from the longissimus dorsi and analyzed for abundance of proteins relating to skeletal muscle catabolism. Data were analyzed as a randomized complete block (date of parturition) design with repeated measures using the MIXED procedure of SAS. Heifers fed HMP increased conceptus-corrected BW by a greater magnitude than CON at day-8 relative to-55 and-41 (treatment × day, P < 0.01). DMI increased (P < 0.01) by 18% on week-2 compared to-8, but then decreased (P < 0.01) by 8.0% for week-1. N-intake, apparent N digestion, N excretion, and N retention (g/d) were all greater (P < 0.01) for HMP heifers than CON but did not differ when expressed as a proportion of N intake. Ruminal NH 3-N decreased (treatment × day, P < 0.01) as parturition approached for HMP (10.1 to 8.6 mg/dL); whereas, NH 3-N was not affected for CON (1.0 to 1.3 mg/dL). Consequently, plasma urea-N was greater (P < 0.01) for HMP heifers (15.0 vs. 7.5 mg/dL). Heifers fed HMP had improved (P < 0.01) DM, OM, and NDF digestibility relative to CON heifers. The abundance of calpastatin was greater (P = 0.03) and calpain tended to be greater (P = 0.085) for CON cows compared to HMP. Feeding greater quantities of MP during late gestation may improve ruminal fermentation, N balance, and improve BW gain prepartum.

Publication date

2019-01-01

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