Response of Cows to Dietary Crude Protein During Midlactation

• Published in: Journal of dairy science 1981-04, Vol.64 (4), p.655-661
• Main Authors: Barney, D.J., Grieve, D.G., Macleod, G.K., Young, L.G.
• Format: Article
• Language: English
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(81)82626-4

At the end of 19 (± 2.65) wk postpartum, 24 multiparous cows were assigned randomly (6 per group) to rations containing 12, 14, 16, and 18% crude protein for a 6-wk experimental period. Prior to the experimental period all cows were fed a 16% protein diet. Treatment means for 12, 14, 16, and 18% protein were for milk yield, 25.3, 25.2, 24.8, 26.4kg; solids-corrected milk, 23.6, 23.5, 24.3, 24.8; and dry matter intake, 19.3, 20.3, 21.9, 20.8. There was a cubic increase in body weight and a linear increase of milk protein percent as ration protein increased. In an associated trial, nylon bags were inserted into four rumen fistulated steers fed a 13% crude protein diet conforming to two 4×4 Latin squares, split plot in time. Nylon bags were inserted into the rumen of each steer following morning feeding and withdrawn 4, 8, 12, 24, and 48h later to compare 1) the four protein rations and 2) the four ration components (corn silage, hay, high moisture shelled corn, and soybean meal) for dry matter and crude protein disappearance across time. Dry matter disappearance did not differ between rations. Crude protein disappearance increased with crude protein percent of rations. Dry matter disappearance of rations across time was greater for corn silage than hay. Both dry matter and protein disappearance were higher for 1) soybean meal than for high moisture corn and for 2) concentrates than roughages.