Over-Feeding Metabolizable Protein Supply in Late Gestation Beef Cattle: Effects on DMI, Ruminal Fermentation, and Performance

The objective was to determine the effect of oversupplying metabolizable protein (MP) pre-partum on DMI, BW, and ruminal fermentation. Twenty-four primiparous crossbred Hereford cows were assigned to a high protein (HP; 140% of MP requirement, n = 12) or control (CON; 100% of predicted MP requirement, n = 12) treatment. Cows were individually fed their treatment diet from d -56 relative to parturition and then were switched to a common diet post-partum. Post-partum cows were individually housed until d 33 following parturition and group-housed by pre-partum treatment thereafter. Dry matter intake was measured throughout the study and summarized by week. Cow BW was measured on d -56, -42, -28, -8, 7, 14, 28, 57, 82, and 112 relative to parturition. Ruminal pH was measured from d -35 to 28, and digesta samples were taken on d -34, -16, 7, and 28 for short-chain fatty acid (SCFA) and ammonia measurements. Data were analyzed as a completely randomized block design using the MIXED procedure of SAS. Fixed included treatment, time, and the two-way interaction, while random effects were cow and block. Time (day or week) was analyzed as a repeated measure. Pre-partum BW of CON did not differ among days; whereas, HP cows increased BW as parturition approached (P = 0.01). Post-partum BW did not differ by treatment or day. Treatment did not affect DMI, but DMI decreased by 7.7% from wk -2 to -1 (P < 0.01), and, post-partum, cows consumed 14.1 and 8.8% less in wk 3 relative to wk 1 and 4 (P < 0.01). Mean ruminal pH was not affected by treatment, but tended to increase (P = 0.06) the week prior to parturition. After parturition, mean ruminal pH decreased from wk 1 to 2 (6.67 vs. 6.40; P < 0.01). Total ruminal SCFA concentration was not affected by treatment during the pre- or post-partum periods, averaging 112 and 120 mM, respectively. However, pre-partum concentrations (mol/100 mol) of isobutyric (0.94 vs. 0.66, P < 0.01), isovaleric (1.03 vs. 0.65, P < 0.01), and valeric acid (1.35 vs. 1.11, P = 0.02) were greater for HP than CON. Pre-partum ruminal ammonia decreased (interaction, P < 0.010) as parturition approached for HP (11.1 to 9.37 mg/dL) whereas, ammonia was not affected for CON (0.88 to 1.26 mg/dL). Overfeeding MP during late gestation may improve ruminal fermentation pre-partum without affecting DMI or BW change post-partum.