Adaptive responses to heat stress, quality of hide and meat from indigenous Nguni and non-descript crossbred cattle

The main objective of this study was to determine the adaptive responses of Nguni and non-descript crossbred cattle (NDCC) to heat stress, nutritionally-related blood metabolite profiles, fatty acid profiles, carcass and meat characteristics, physico-mechanical properties of automotive upholstery crust leather and the associated collagen fibre architecture of hides and crust leather. Forty steers (20 Nguni and 20 NDCC) which were approximately 14 months of age with live weights ranging between 153 kg and 203 kg at the beginning of the study were used. Environmental variables (ambient temperature, relative humidity, wind parameters, solar radiation) were collected from a weather station at the research farm. Temperature-humidity index (THI) values were computed. Rectal and skin temperature, skin traits and blood metabolites were determined at two-week intervals over 16 weeks. Hair coat scores ranged from extremely short (score 1) to very woolly (score 7). At slaughter, blood samples were collected after exsanguination. Meat samples were collected from the right muscularis longissimus thoracis et lumborum (LTL) and Triceps brachii (TB) muscles after 24 hours of chilling of carcasses for physico-chemical quality tests. Fatty acid profiles and physico-chemical quality of meat were determined on the LTL and TB. An additional fifty-four hides (27 Nguni and 27 NDCC) were obtained from a commercial abattoir at slaughter. The hides were tanned into automotive crust leather and tested for physico-mechanical quality. Results showed that week and environmental variables affected skin temperature; also, the rectal and skin temperatures were negatively correlated to body condition, skin pigment, coat score and skin thickness. Non-descript crossbred cattle had higher coat scores (2.1 ± 0.36 to 4.1 ± 4.20) than Nguni cattle (1.6 ± 0.36 to 4.1 ± 0.36). Body condition scores, blood creatinine, urea, total protein, albumin and globulin were affected by genotype and week of sampling. At the end of the trial, NDCC had higher slaughter and hide weights (285.9 ± 6.52 kg and 18.4 ± 0.54 kg, respectively) than Nguni cattle (232.6 ± 6.5 kg and 14.7 ± 0.54 kg, respectively). The majority of NDCC carcasses (73.7 percent) had a fatness level of 1 compared to Nguni carcasses (50 percent). Intramuscular fat was higher in Nguni (1.8 ± 0.09 percent) compared to NDCC (1.5 ± 0.09 percent) steers. Nguni steers had darker muscle colour (L*=33.6 ± 0.01) than NDCC (L*= 35.7 ± 0.54). Nguni and NDCC had similar thawing loss, cooking loss, WBSF tenderness, fat-free dry matter, moisture content, fatty acid profiles and health-related lipid indices. Ultimate muscle pH, meat colour and chroma were similar in the LTL and TB. Concerning the skin, Nguni and NDCC had similar physico-mechanical properties. However, breaking load and tensile strength were higher (1257.1 ± 70.72 N and 28.3 ± 1.23 MPa) in samples taken parallel to the backbone compared to that taken perpendicular to the backbone (979.5 ±70.72 N and 23.6 ±1.23MPa) across the two genotypes. Non-descript crossbred crust leather varied in physico-mechanical tests by direction of sampling. Collagen fibre orientation in hides and crust samples also varied between longitudinal and cross-sections. Collagen fibre diameters in the Nguni were similar in longitudinal and cross-sections (3.4 ± 0.12 μm and 3.2 ± 0.11 μm, respectively). From this study, it is concluded that THI, hair coat, skin traits and body condition affect skin temperature, but not rectal temperature, cortisol and CK activity in Nguni and NDCC reared extensively. The two genotypes differ in nutritionally-related blood metabolites, growth performance, hide weights and carcass traits. Beef from Nguni and NDCC differs in the IMF and meat lightness but is similar in the meat fatty acid composition and some physico-chemical quality parameters. Automotive crust leathers from the two genotypes were similar in some physico-mechanical properties. Collagen architecture varied among different regions of hides and crust leather