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Effect of Increasing Protein and Fat Inclusion in the Diet of Beef Cows During Gestation and Lactation on Performance, Milk Production, Pregnancy Rate, and Pre-Weaning Progeny Growth
This study was conducted to evaluate the effects of increasing CP and fat inclusion in the diets of Angus x Simmental cows (610 ± 16.8 kg; n=48) pregnant with male progeny during late gestation through mid lactation on cow performance and pre-weaning calf growth. Cows were allotted by BW and BCS to four treatments arranged in a 2 x 2 factorial, with two CP (11.9 and 17.1%; LP and HP diets, respectively) and two fat concentrations (2.0 and 4.8%; LF and HF diets, respectively) in the diet DM. Cows were housed for 178 d in individual pens and fed rations formulated to be isocaloric. The average calving date was on d 85 ± 7.2. After the treatment period, cow-calf pairs were placed on pasture and managed as one group until weaning (d 279). Performance and milk production data were analyzed using the MIXED procedure of SAS. Pregnancy rate data were analyzed using the GLIMMIX procedure of SAS. Cows fed LP and HF had lower (P<0.01) BW gains through 178 d compared to cows fed HP and LF, respectively, and BW gain for LP cows was much lower when HF diets were fed compared to LP cows fed LF diets (interaction; P<0.01). In contrast, BW gain from d 179 to weaning was greater (P<0.01) for LP and HF compared to HP and LF, respectively, and BW gain for LP cows was much greater when HF diets were fed compared to LP cows fed LF diets (interaction; P≤0.01). Body condition score and DMI on d 178 and from d 86 through 178, respectively, were greater (P<0.01) for HP only when cows were fed the HF diet. In all periods, G:F was greater (P<0.05) for cows receiving HP diets within both dietary fat inclusions. Milk production was greater for cows receiving HP and LF (P≤0.02) diets compared to LP and HF, respectively. Moreover, milk fat, true protein, urea nitrogen, and total solids were greater (P≤0.05) for cows fed HP compared with those fed LP. No effects of dietary CP or fat concentrations were observed for TAI (P=0.11) and overall (P=0.99) pregnancy rates, as well as for calf BW and ADG. In summary, increasing dietary CP inclusion had positive effects on cow performance, milk production, and milk composition. In contrast, with the exception of TAI, increasing fat inclusion had either neutral or negative effects on the analyzed variables.
Keywords: developmental programming; maternal nutrition; milk composition