Effects of metabolizable protein supplementation and intake on cow production
Nichols, Bryan Micheal
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In 2008, two-yr-old Angus and Simmental x Angus pregnant, non-lactating heifers (n = 120, initial BW = 448 ± 36 kg) had individual feed intake determined using a GrowSafe feeding system. Dietary treatments were based on approximately 85% grass hay and 15% supplement. Supplements contained whole soybeans plus corn (102% MP) or dried distillers grains plus soybean meal (119% MP). After 35 d of intake measurement, heifers were placed into adjacent pens and fed their diets for an additional 50 or 82 d. Upon completion of the feeding trial, heifers were transported back to the ranch, managed as a single group, and production data were measured. Level of dietary MP had no effect (P > 0.17) on calf birthweight, adjusted 205-d weight, preweaning ADG, age at weaning, cow BW at calving, proportion of cows cycling at bull exposure, or proportion of cows to conceive. Dry matter intake per unit of BW 0.75 and RFI did not differ because of treatment and had no effect (P > 0.17) on any variables measured. In 2009, 24 of these heifers that had the highest and lowest RFI were selected to be fed a similar diet as in 2008 to determine the correlation of DMI per BW 0.75 and RFI between heifers (2008) and later as cows (2009). Cows were adapted to the diet for 10 d followed by a 70 d trial to determine individual feed intakes and weight gain. Dry matter intake per BW 0.75 was highly correlated (r = 0.71, P < 0.01) between first and second parities, as was residual feed intake (r = 0.83, P < 0.01). For 5 d, fecal samples were collected twice daily and indigestible ADF was used to estimate DM digestibility. Residual feed intake was negatively correlated with DM digestibility (r = -0.51, P = 0.03). Production traits from 2008 were analyzed to determine if cows found to be either high or low RFI in 2009 had similar levels of production. Low and high RFI cows did not differ (P > 0.45) in cow BW at calving, calf birthweight, calf ADG, 205-d weaning weight, or weaning age.