Effects of feeding juniper as a roughage on feedlot performance, carcass measurements, meat sensory attributes, and volatile aroma compounds of yearling Rambouillet wethers

Authors: KERTH, CHRISTOPHER - Texas A&M University; WALL, KAYLEY - Texas A&M University; MILLER, RHONDA - Texas A&M University; WHITNEY, TRAVIS - Texas A&M Agrilife; STEWART, WHITNEY - University Of Wyoming; BOLES, JANE - Montana State University; Murphy, Thomas - Tom

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2019
Publication Date: 5/17/2019
Citation: Kerth, C.R., Wall, K.R., Miller, R.K., Whitney, T.R., Stewart, W.C., Boles, J.A., Murphy Jr, T.W. 2019. Effects of feeding juniper as a roughage on feedlot performance, carcass measurements, meat sensory attributes, and volatile aroma compounds of yearling Rambouillet wethers. Journal of Animal Science. 97(7):2816-2830. https://doi.org/10.1093/jas/skz174.
DOI: https://doi.org/10.1093/jas/skz174

Interpretive Summary: Estimated per capita disappearance of sheep meat in the U.S. is currently less than 1 pound per year, the lowest of any major livestock species. In relation, estimated domestic per capita disappearance of chicken, beef, and pork is 90.8, 54.4, and 47.0 pounds per year, respectively. Sheep meat is classified according to predictors of animal age at harvest: lamb (< 1 year of age), yearling mutton (1 to 2 years of age), and mutton (> 2 years of age). Flavor is considered one of the most important factors contributing to the consumer acceptance of sheep meat. Therefore, identifying biological and environmental effects that contribute to flavor is an important component to improving domestic per capita consumption of sheep meat products. Past studies have attributed differences in sheep meat flavor to pre-harvest diet and breed, but the most consistent indicator is age. Older animals tend to have a greater concentration of off-flavor compounds present in their adipose tissue, which can contribute to a negative eating experience for many consumers. Nevertheless, market volatility can discourage sheep feeders from marketing animals at an appropriate age, resulting in a greater proportion of older animals being marketed in certain seasons. There is evidence that secondary compounds present in certain plants may reduce certain off-flavor characteristics in sheep meat and enhance consumer eating experience. Juniper, a woody plant with high secondary compound content, can encroach on grazing lands and is difficult to manage in many regions of the country. Researchers at Texas A&M University have determined that juniper can be harvested cheaply and incorporated as a roughage source in ruminant diets, replacing traditional feeds such as hay without negative impacts on animal performance and health. The present study evaluated performance, carcass measurements, and meat sensory characteristics of yearling wethers (~18 months of age at harvest) fed 20% juniper for 20 or 40 days prior to harvest compared to a 20% hay treatment. While feeding juniper did not enhance sensory characteristics in meat, juniper fed animals had similar performance and carcass measurements to the hay treatment. Furthermore, the sensory taste panel did not detect consistent off-flavors in meat from any of the animals. Results indicate that properly prepared yearling mutton has consumer value and reiterates findings that incorporating juniper into ruminant diets is a sustainable approach to reducing its negative impact on grazing lands.

Technical Abstract: The majority of U.S. lambs are born during late winter or early spring, which can create downstream variability in carcass quality if commercial lamb harvest is to be relatively constant throughout the year. Flavor is an important quality determining haracteristic of sheep meat and is influenced, in part, by animal age at harvest. However, management practices to mitigate the risk of objectionable flavors in meat from old crop lambs or yearlings are not well known. Yearling (16.8 ± 0.14 mo) Rambouillet wethers were assigned to 1 of 3 treatment groups, which consisted of feeding a 20% ground sorghum-sudangrass hay diet for 40 d (JUN0; n = 10), a 20% ground juniper diet for 40 d (JUN40; n = 10), or a 20% ground hay diet for 20 d followed by a 20% ground juniper diet for 20 d (JUN20; n = 10). Wethers were harvested on day 41 and a whole bone-in loin and a boneless inside leg roast were fabricated from one side each of carcass. After grilling (loin chop) or convection air roasting (leg roast), trained sensory panel evaluation and measurement of aroma volatiles by gas chromatography/mass spectrometry were performed. Treatment diet did not affect (P = 0.17) wether feedlot performance, dressing percentage, or loin eye area. However, wethers fed JUN0 tended (P = 0.06) to have greater back fat depth than wethers fed JUN20 or JUN40. No trained sensory panel trait of loin chop samples was affected (P > 0.10) by treatment. Leg roasts from JUN0 and JUN20 wethers had greater (P = 0.01) lamb identification sensory score than JUN40. Benzaldehyde, 1-heptanol, and 1-octanol concentrations were greater (P < 0.05) and decanal and nonenal concentrations were less (P < 0.05) in loin chops from JUN0 compared with JUN40 wethers. Additionally, the terpenes cedr-8-ene, gamma muurolene, and widdrene tended to be greater (P < 0.07) in loin chops from JUN20 and JUN40 than JUN0 wethers. The 2-pentyl-furan concentrations were greatest (P = 0.03) in leg roasts from JUN40 wethers. Like the loin chops, cedr-8-ene, gamma-muurolene, toluene, and widdrene were greater (P < 0.05) in leg roasts from wethers fed either of the juniper diets compared with JUN0. Yearling wethers can be finished on a feedlot diet containing 20% juniper for up to 40 d prior to harvest with no impact on feedlot performance, carcass characteristics, nor negative impact on sensory attributes or volatile compounds of either grilled loin chops or roasted legs.