441 - The Influence of Diet Type on Ranking for Feed Intake in Angus Cows

The objective of this study was to determine the effect of diet type on feed intake in mature Angus cows. Forty-eight gestating Angus cows (708 ± 52 kg; 7 ± 0.75 years old) were assigned to one of four drylot pens based on their genomic score for residual feed intake (“High” RFI, 7.3 ± 0.5, “Low” RFI, 5.5 ± 0.7). Each pen contained an automatic waterer as well as four GrowSafe individual feed intake units. During the first period, two of the four pens were assigned to a processed hay diet (10.0% CP, 1.98 Mcal ME/kg DM) while the other two pens consumed a mixed ration consisting of 43.0% hay, 33.0% corn, 13.0% soybean hulls, and 11.0% liquid supplement, DM basis (11.7% CP, DM basis and 2.43 Mcal ME/kg DM). Following a 14-day adaptation period, feed intake was recorded for 45 days. Subsequently, diet type was switched and followed by 14 days of adaptation to the new diet and 45 days of feed intake measurement. Data were analyzed as a crossover study using the GLIMMIX procedure in SAS v9.4. Pearson correlation coefficients were determined between phenotypic traits and genomic score. Feed intake was highly correlated (r = 0.75) among the two diet types. In comparison, average daily gain (ADG) was negatively correlated (r = -0.37) among the two diet types. No differences were observed in DMI or performance for cows ranked “high” or “low” based on genomic score. More research is required to determine if selection for increased weight gain when consuming a high-quality mixed ration could be detrimental to cattle performance consuming moderate to low-quality forage.