To investigate the effect of heat stress (HS) on production and metabolism of Afshari sheep, 32 intact male lambs (33.2 ± 4.5 kg) were used in a completely randomized design using 2 experimental periods. In period 1 all 32 lambs were housed in thermal neutral (TN) conditions (25.6 ± 2.6°C and a temperature-humidity index [THI] of 72.0 ± 2.6) and fed ad libitum for 8 d. In period 2 (P2; 9 d), 16 lambs were subjected to cyclical HS (29.0 to 43.0°C and a THI ≥80 for 24 h/d) and the other 16 lambs were maintained in TN conditions but pair fed (pair-fed thermal neutral [PFTN]) to the HS lambs. During each period DMI and water intake were measured daily. Respiration rate, rectal temperature, and skin temperature at the shoulder, rump, and front and rear leg were recorded at 0700 and 1400 h daily. Water intake increased (P < 0.05) during P2 in both HS and TN lambs (88 and 35%, respectively). Heat stress increased the 0700 and 1400 h surface temperature at the shoulder (3.0 and 10.6%), rump (2.7 and 12.7%), rear leg (3.1 and 13%), and front leg (3.0 and 13%) and respiratory rates (72 and 124%; P < 0.01, respectively, for 0700 and 1400 h) but only the 1400 h rectal temperature was increased (P < 0.01; 0.54°C) in HS lambs. Plasma glucose concentration decreased in P2 (P < 0.01) in both the HS and PFTN lambs. Basal insulin concentrations decreased in PFTN controls but increased in HS lambs (environment × period interaction; P < 0.05). Blood urea nitrogen concentration was not affected by environment or period, but NEFA levels were slightly elevated (P < 0.01) in both PFTN and HS lambs during P2. Interestingly, HS did not affect DMI, but ADG was reduced (36%; P < 0.01) compared to the PFTN lambs. These results indicate that the direct effects of heat (not mediated by reduced DMI) are partially responsible for reduced growth in heat-stressed lambs.

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There is a growing interest in odd- and branched-chain fatty acids (OBCFA) in milk following reports that several branched-chain fatty acids (FA) have health promoting effects, and certain milk OBCFA could serve as a biomarker to assess ruminal function. Twenty-four Holstein cows were fed 3 low-forage diets containing 30 g/kg of dry matter of prilled palm fat (PPF), sunflower oil (SO), or an equal mixture of both fats (experiment 1) or 3 diets containing 30 g/kg of dry matter of SO with a forage-to-concentrate ratio of 39:61, 44:56, or 48:52 (Experiment 2); diets were fed to investigate milk OBCFA composition and to explore the relationships between ruminal VFA and milk OBCFA using principal component analysis. Including SO in diets decreased yields of milk 13:0 anteiso, 15:0 anteiso, 15:0, 17:0, cis-9 15:1, and cis-9 17:1 compared with PPF. The molar proportion of ruminal propionate was the lowest and the yields of milk 14:0 iso and 16:0 iso were the greatest with the diet containing both fat supplements. Replacing concentrate with forages linearly increased ruminal acetate and yields of milk 13:0 iso, 14:0 iso, 15:0 iso, 16:0 iso, 17:0 iso, 13:0 anteiso, 15:0 anteiso, 15:0, 17:0, cis-9 15:1, and cis-9 17:1. The principal component analysis revealed that ruminal molar proportion of acetate related to concentrations of milk iso FA containing <17-carbon, whereas ruminal propionate related to milk 15:0, 17:0, cis-9 15:1, and cis-9 17:1, with the stronger correlations between milk OBCFA and ruminal acetate than propionate. No associations were found between ruminal molar proportion of butyrate and milk OBCFA concentrations. The results suggest that complete replacement of PPF with SO at 30 g/kg of dry matter in low-forage diets is not an effective strategy to enhance bioactive branched-chain FA in milk, rather this feeding practice lowers anteiso FA in milk; however, increasing forage proportion in diets containing SO enhances several iso and anteiso FA in milk. The milk OBCFA concentrations have stronger correlations with ruminal acetate molar proportion than with propionate or butyrate in cows fed diets containing supplemental fats.

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