Abstract
The objectives of this study were to evaluate the effect of diet type on feed intake, animal performance and intake rank in mature, gestating Angus cows (130 ± 13 days pregnant at trial initiation) and to identify differentially expressed genes (DEG) associated with each diet type. Forty-eight gestating commercial Angus cows (708 ± 52 kg of body weight [BW]; 7 ± 0.75 years old) were assigned to one of two diet sequences, concentrate-forage (CF) or forage-concentrate (FC), representing the order in which the two diets were consumed. In the first period, two of the four pens were assigned to the CF sequence and two to the FC sequence. Each pen contained an automatic waterer as well as four GrowSafe® feed intake units (GrowSafe System Ltd., Airdire, Alberta). The forage diet consisted of 100% processed hay (10.0% CP, 1.98 Mcal ME/kg dry matter [DM]) while the concentrate diet consisted of 43.0% hay, 22.0% corn, 24.0% soybean hulls, and 11.0% supplement on a DM basis (11.7% CP, DM basis and 2.43 Mcal ME/kg DM). Following a 14-day adaptation period, feed intake and BW gain were recorded for 56 days. Subsequently, diet type was switched and followed by 14 days of adaptation to the new diet and 48 days of feed intake and BW gain measurement. Intake and performance data from this crossover study were analyzed using mixed model methods in SAS v9.4. There was a diet by period interaction (P < 0.01) for daily gain (ADG) with cows in the FC sequence gaining more weight than expected while consuming forage. Spearman rank correlation for dry matter intake was 0.70 (P < 0.01) for FC cows and 0.36 (P < 0.1) for CF cows. In contrast, there was no significant relationship for ADG among the two diet types, regardless of sequence (P > 0.4). In total, RNA sequencing of muscle tissue from the first period identified DEG associated with diet type. Enriched biological processes were identified by functional enrichment analysis of the DEG using g: Profiler and were primarily associated with energy metabolism and lipid biosynthesis. The results of this study support the hypothesis that gene expression in muscle responds differently when cows consume low-quality forage versus high-quality, energy-rich diets, even though feed intake rank correlations were high in the FC sequence and moderate in the CF sequence.