Abstract

The objective of this study was to determine the chemical composition and in situ degradability of dry matter (DM), crude protein (CP), acid detergent fiber (ADF), and neutral detergent fiber (NDF) of stockpiled perennial forage (SPF) or sun-cured hay (HAY) when collected at the start or end (October vs. December) of fall grazing. Selected 6, 4-ha paddocks consisting of meadow bromegrass and alfalfa, were randomly assigned to 1 of 2 replicated (n = 3) winter feeding systems (SPF and HAY). Sampling was done twice per year at the beginning (October) and end (December) from (a) stockpiled perennial forage (SPF) in field paddocks and from (b) harvested round bale hay (HAY) over 2 consecutive years. Selected 6, 4-ha paddocks consisting of meadow bromegrass and alfalfa, were randomly assigned two winter feeding systems (SPF (n=3) and HAY (n=3)). Sampling were done twice per year at the beginning (October) and end (December) from (a) SPF (b) HAY over 2 consecutive years. To evaluate in situ degradability, duplicate nylon bags from each experimental unit were incubated for 0, 3, 6, 10, 13, 25, 48, 72, and 96 h in five Hereford heifers fitted with rumen cannula. Relative to HAY, SPF had greater (p = 0.01) OM (906 vs. 916 g/kg DM) and NDF (653 vs. 631 g/kg DM) concentrations. Sampling date had no effect (p > 0.05) on CP, OM, and ADF in both forages, whereas the NDF was greater (p = 0.01) in forages sampled in December. The in situ soluble fraction (S) of DM was greater (p = 0.01) for SPF collected in October, HAY collected in October, and HAY collected in December s (156, 138, and 152 g/kg DM, respectively) relative to SPF collected in December (106 g/kg DM). The potentially degradable fraction (D) of CP was less (p < 0.05) for HAY December samples compared to SPF December and HAY October samples (257 vs. 522 and 523 g/kg CP, respectively). The SPF had a greater (p < 0.05) potentially degradable ADF (749 vs. 587 g/kg ADF) and potentially degradable NDF (770 vs. 591 g/kg NDF) compared to HAY. The effect of forage type and sampling date did not affect (p > 0.05) effective degradability of NDF. Regardless of the forage type the potentially degradable fraction of NDF decreased from October to December (SPF: 770 to 730 g/kg NDF) (HAY: 680 g/kg to 491 g/kg NDF). These findings suggest SPF grazing is a robust substitute to hay feeding systems for beef cows.

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