| Resum: |
In the present thesis, 3 experiments were carried out using Murciano-Granadina dairy goats under low temperature (LT; Exp. 1) and heat stress (HS; Exp. 2 and 3) conditions in order to evaluate the physiological, metabolic, productive and behavioral responses. In Exp. 1, 8 dairy goats in mid-lactation were randomly allocated into 2 groups: thermal-neutral (TN; 15 to 20°C) and LT (-3 to 6°C) in a crossover design with 2 treatments in 2 periods (21 d each). Body weight, feed intake, water consumption, milk production, rectal temperature (RT), respiratory rate (RR), as well as blood insulin, glucose, non-esterified fatty acids (NEFA), beta- hydroxybutyrate (BHB), cholesterol and triglycerides were measured. Compared to TN goats, LT goats had similar feed intake, but lower (P < 0. 05) water consumption (−23%), RR (−6 breaths/min) and RT (−0. 32°C). Milk of LT goats had greater (P < 0. 05) contents of protein (+10%), fat (+12%) and lactose (+4%) than TN goats. The LT goats lost −0. 45kg BW, whereas TN goats gained 2. 2 kg (P < 0. 05). Values of blood glucose, NEFA, hematocrit and hemoglobin increased (P < 0. 05) by LT, whereas BHB and triglycerides decreased (P < 0. 05). In Exp. 2, 30 dairy goats were exposed to 2 treatments: TN (15 to 20°C), and HS (30 to 37°C) from 12 days before mating to day 45 of gestation. Feed intake, RT and RR were recorded. After kidding, litter size, birth weight and weaning weight of kids were registered. At 27 4 days old, female kids exposed to in utero TN (IUTN; n = 16) and HS (IUHS; n = 10) were subjected to 2 tests: arena test (AT) and novel object test (NOT). In both tests, kids were entered a 4x4 m2 arena and the distance travel, number of squares entered, jumps and sniffs of the arena were recorded. At 8 months old, a subset of growing goats (n = 8) from each group (IUTN and IUHS) were exposed to 2 environmental conditions in 2 consecutive periods: a TN period for 7 d at 15-20 °C (P1), and then HS for 21 d at 30-37°C (P2). Feeding behavior and other activities (drinking, exploring, and grooming) and resting behaviors, as well as posture were recorded. Compared with TN, gestation length was shortened by HS (-3d; P < 0. 01). In the AT, IUHS kids showed a lower number of sniffs (P < 0. 01) than IUTN. Further, during HS (P2), both IUTN and IUHS goats spent more time resting, panting and drinking (P < 0. 001) with no differences between both groups. In Exp. 3, the same goats (IUTN; n =8, and IUHS; n = 8) used for HS behavior in Exp. 2 were used. Body weight, feed intake, water consumption, RT, RR as well as blood glucose, insulin, NEFA, BHB, cholesterol and triglycerides were measured. In addition, 4 goats from each treatment were subjected to a glucose tolerance test (GTT), insulin tolerance test (ITT), and an epinephrine challenge, each one performed once during P1 and P2. Regardless the in utero thermal treatment, HS resulted in increased (P < 0. 01) RT, RR and water consumption, but decreased (P < 0. 05) body weight gain. However, IUHS goats needed 10% less (P < 0. 05) RR to keep similar RT to IUTN goats. Compared to IUTN, IUHS goats had greater glucose area under curve at 45 min (P = 0. 077) and 90 min (P = 0. 056), and lower (P < 0. 05) insulin clearance rate in response to the GTT. In conclusion, LT goats had similar DM intake to TN goats, but their milk contained greater fat and protein. The LT goats covered the extra energy needed for heat production by mobilizing body fat reserves as indicted by greater blood NEFA levels. Heat stress during the first third of pregnancy shortened pregnancy length, and modified some behavioral, physiological and metabolic responses to various stimulators, including HS during the postnatal life. |
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