Submitted to: Sheep and Goat Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 20, 1997
Publication Date: N/A
Interpretive Summary: In some areas of the U.S., such as the mid-South, moderate to low quality hay is fed by many livestock producers for a major portion of the year when tropical grasses are not actively growing. Thus, information regarding differences among potential grasses and various hay harvesting schemes in nutritive value for gestating ruminants is needed. Also, abilities of various sheep breeds and crosses to consume high quantities of digestible nutrients with low-quality, tropical grasses, which frequently are consumed in gestation, are unknown. Effects on intake and digestibility of grass source (i.e., Eastern gamagrass vs switchgrass) and hay cutting treatment were similar among breed groups, and grass chararacteristics impacting feed intake were affected by hay cutting treatment differently between grass sources. St. Croix and St. Croix-Romanov crosses may be better suited for early to mid-gestation consumption of such tropical grass hay sources compared with St. Croix- Texel crosses, and Gulf Coast Natives may require supplementation for body weight maintenance. These results are important because Eastern gamagrass and switchgrass are tropical grasses grown in the midwestern and eastern U.S., although previously little knowledge existed regarding nutritive value for sheep of these grasses in the mid-South. Furthermore, sheep breeds and crosses most suited for production in the mid-South differ from those adapted to other areas, and little information was present concerning digestible nutrient intake by sheep genotypes for the mid-South.
Technical Abstract: Mature ewes (24; 21 months of age), of four breed groups (St. Croix, St. Croix x Romanov, SR; St. Croix x Texel, ST; Gulf Coast Native, N) and in early to mid-gestation, were used (4 x 2 x 3 factorial; eight simultaneous 3 x 3 Latin squares) to determine effects and interactions in feed intake and digestibility of breed group, tropical grass source (Eastern gamagrass, GG; switchgrass, SG) and hay cutting treatment (1=primary growth harvested on June 12, 1995; 2=primary growth harvested on August 14, 1995; 3=regrowth from June 12 to August 14, 1995). Soybean meal was supplemented, and body weight (BW) was 39, 49, 46, and 59 kg (SE 2.5) for S, SR, ST and N, respectively. Interactions between breed groups and dietary forage treatments did not occur (P>0.10). Hay dry matter intake ranked (P<0.05) hay cutting treatment 3>2>1 for GG and 2<1 and 3 for SG (59, 50, 67, 49, 38, and 46 g/kg BW/0.75 for S, SR, ST, and N, respectively y(SE 2.6). Hay organic matter digestibility was greater (P<0.05) for GG vs SG and for cuttings 1 and 3 vs 2. Digestible hay organic matter intake differed among treatments as noted for hay intake (28.1, 20.1, 32.8, 16.8, 8.0, and 14.8 g/kg BW/0.75 for GG-1, GG-2, GG-3, SG-1, SG-2, and SG-3, respectively; SE 1.22), and was 23.1, 23.5, 19.0, and 14.9 g/kg BW/0.75 (SE 1.63) for S, SR, ST, and N, respectively. In conclusion, effects on intake and digestibility of grass source and hay cutting treatment were similar among breed groups, and grass characteristics impacting feed intake were affected by hay cutting treatment differently between GG and SG. St. Croix and SR may be better suited for early to mid-gestation consumption of such tropical grass hay sources compared with ST and N may require supplementation for BW maintenance.