The objective of this study was to determine the activity of steroid- and eicosanoid-metabolizing enzymes in horses with varying BCSs. The BCSs of twenty non-pregnant, anoestrous mares were determined prior to euthanasia, and tissue samples were collected from the liver, kidney, adrenal gland, ovary and endometrium. Cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A) and uridine 5'-diphospho-glucuronosyltransferase (UGT) activities were determined using luminogenic substrates. The MIXED procedure of SAS was used to test the effect of BCS on enzyme activity and differences between tissues. Activity of CYP1A in adrenals was increased (p ≤ .05) in BCS 5 versus BCSs 4 and 6. Activity of CYP1A in the liver was increased (p = .05) in BCS 4 versus BCSs 5 and 6. Activity of CYP1A was 100-fold greater (p < .0001) in the liver than in the adrenal, ovary and kidney. Activity of CYP2C was 100-fold greater (p < .0001) in the liver than in the adrenal, ovary and endometrium. Activity of CYP3A was only detectable in the liver. Activity of UGT in the kidney was decreased (p = .02) in BCS 4 versus BCSs 5 and 6. Activity of UGT was threefold greater (p < .0001) in the liver than in the kidney, whereas activity of UGT was ninefold greater (p < .0001) in the kidney than in the ovary and endometrium. In general, BCS did not alter the activity of steroid- and eicosanoid-metabolizing enzymes in horses. However, tissue differences in these enzymes indicated abundant hepatic metabolism in horses, which is similar to other livestock species.

Optimal use of native warm-season grasses in pasture systems involves stocking grazing livestock at suitable rates. The study objective was to evaluate forage nutritive value and heifer ADG at two stocking rates on mixed-sward pastures of big bluestem (Andropogon gerardi Vitman), little bluestem (Andropogon scoparius), and indiangrass (Sorghastrum nutans L.). Pastures (3 replications) were stocked for 56 d during June and July in 2 yr with crossbred (Bos taurus) heifers (n = 24 heifers/year) stratified by initial BW (288.3 ± 1.7 kg) to one of two continuous stocking rates: 1.9 heifers/ha (HIGH) and 1.2 heifers/ha (LOW). Mean forage nutritive values on a DM basis were not different between HIGH and LOW stocking rates, respectively, for CP (7.0 ± 0.2% vs 6.7 ± 0.2%; P = 0.27), ADF (41.0 ± 0.6 vs. 41.4 ± 0.6; P = 0.64), NDF (69.9 ± 0.5 vs. 68.7 ± 0.5; P = 0.09), or relative feed value (RFV) (76.0 ± 1.0 vs. 76.9 ± 1.0; P = 0.53). There was a year effect (P &lt; 0.01) and stocking rate x day effect (P &lt; 0.01) for TDN. At LOW, TDN decreased from day 0 to day 28 (P = 0.02) and day 28 to day 56 (P = 0.02). At HIGH, TDN decreased (P &lt; 0.01) from day 0 to day 28 but remained steady until day 56 (P = 0.21). There was a stocking rate x day interaction (P &lt; 0.01) with ADG: LOW day 28 to 56 (1.20 ± 0.08 kg/day), HIGH day 0 to 28 (0.89 ± 0.08 kg/day), HIGH day 28 to 56 (0.44 ± 0.08 kg/day), and LOW day 0 to 28 (0.30 ± 0.08 kg/day). Further assessment of cattle ADG using more divergent stocking rates and plant persistence measures is warranted to inform ideal native grass stocking rate recommendations.

Native grasses are touted for use in drought mitigation strategies for grazing cattle. It is important to determine how these forages compare in specific production environments to more widely used improved grasses such as bermudagrass [Cynodon dactylon (L.) Pers.] that they may replace as pasture. Native warm-season grasses including big bluestem (Andropogon gerardi Vitman), little bluestem (Andropogon scoparius), and indiangrass (Sorghastrum nutans L.) were evaluated against bermudagrass pastures in the Black Belt Prairie region of Mississippi for stocker cattle grazing. Objectives were to compare bermudagrass (BG), indiangrass (IG) and mixed-sward native warm-season grass (mix of big bluestem, little bluestem, and indiangrass) (NGMIX) pasture for forage nutritive value and steer ADG. Crossbred (Bos taurus) steers (n = 36 steers/year) were stratified by initial BW (339.7 ± 4.3 kg) to 2.02-ha pastures (3 replications) during 56-d grazing periods in June and July for 2 yr. Mean forage nutritive values on a DM basis were: BG [8.8% CP, 43.4% ADF, 67.3% NDF, 58.7% TDN, and 77 relative feed value (RFV)], IG (6.7% CP, 39.6% ADF, 68.3% NDF, 58.2% TDN, and 79 RFV) and MIXNG (7.3% CP, 40.5% ADF, 69.5% NDF, 58.1% TDN, and 77 RFV). A forage treatment x day x year effect existed (P &lt; 0.01) for each these nutritive values. There was no effect (P = 0.47) of forage treatment on steer ADG (BG: 0.4 ± 0.1 kg/d; IG: 0.5 ± 0.1 kg/d; NGMIX: 0.5 ± 0.1 kg/d). Thus, no net advantage or disadvantage in steer growth rates was observed due to forage species. Other factors such as forage establishment cost and animal stocking rates supported may be relevant to consider in decisions to replace bermudagrass with warm-season native grasses.

Pastured cattle are sometimes offered multiple separate salt (NaCl)-containing nutritional supplements. This study objective was to determine how range meal presence impacts mineral supplement intake when cattle choose between multiple salt source offerings. Weaned Bos taurus crossbred steers (n = 24) (initial BW = 263 ± 4.0 kg) were stratified by BW in a completely randomized design across 4 pens with 2 GrowSafe bunks per pen with ad libitum access to mixed-grass pasture and 1) one bunk supplied with a mineral supplement containing 15.0% salt (Grazer Hi/Se Hi/Cu CTC 2800; Multi-Kare, Inc., Tifton, GA) (MINERAL) or 2) one bunk containing a 2:1 range meal containing 30% salt and 13% CP (HI-GRAIN RANGE MEAL 1–2; Land O’Lakes Purina Feed LLC, Shoreview, MN) and the other bunk containing the mineral supplement (RM2) (Exp. 1). In Exp. 2 the 2:1 range meal was replaced with a 3:1 range meal containing 22.5% salt and 15% CP (HI-GRAIN RANGE MEAL 1–3; Land O’Lakes Purina Feed LLC, Shoreview, MN) (RM3). After a 14-d acclimation period intake was monitored for 42 days for Exp. 1 followed by a 7-d acclimation and Exp. 2 spanning 42 days. Mean daily DMI per steer were 104.6 ± 22.7 g and 525.8 ± 228.0 g of the 2:1 and 3:1 range meal, respectively. In Exp. 1 steer daily DMI was greater (P &lt; 0.01) for MINERAL (31.9 ± 2.2 g) than for the mineral portion (4.3 ± 2.2 g) of RM2. Mean steer daily DMI in Exp. 2 was greater (P &lt; 0.01) for MINERAL (57.2 ± 6.1 g) than the mineral portion (3.4 + 6.1 g) of RM3. Range meal offered separately and simultaneously with a salt-containing mineral supplement decreases mineral supplement consumption by severalfold with implications for potential inadequate daily intake of nutrients and medications mixed in these supplements.

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