Resumen de Effects of thermal stress on dairy goats and their offspring
Wellington Napoleon Coloma Garcia
In this thesis, 3 experiments were performed using Murciano-Granadina dairy goats under low temperature (LT; Exp. 1) and heat stress (HS; Exp. 2 and 3) conditions to evaluate the physiological, metabolic, productive and behavioral responses. In Exp. 1, 8 goats in mid-lactation were randomly allocated into: thermal-neutral (TN; 15 to 20°C) or LT (-3 to 6°C) in a crossover design with 2 treatments in 2 periods (21 d each). Body weight (BW), feed intake, water consumption, milk production, rectal temperature (RT), respiratory rate (RR), and 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). Blood glucose, NEFA, hematocrit and hemoglobin values increased by LT, whereas BHB and triglycerides decreased (P < 0.05). In Exp. 2, 30 goats (n = 15) were exposed to: TN (15 to 20°C), or HS (30 to 37°C) from 12 d before mating to day 45 of gestation. Feed intake, RT and RR were recorded. After kidding, litter size, kid birth weight and weaning weight were registered. At 27 ± 4 d old, female kids exposed to in utero TN (IUTN; n = 16) and HS (IUHS; n = 10) were subjected to: arena test (AT) and novel object test (NOT). In both tests, kids were entered a 4x4 m2 arena and distance travel, number of squares entered, jumps and arena sniffs were recorded. At 8 months old, a subset of growing goats (n = 8), from IUTN and IUHS, were consecutively exposed in 2 periods to: TN period for 7 d at 15-20 °C (P1), and then HS for 21 d at 30-37°C (P2). Feeding and resting behaviors, other activities (drinking, exploring, and grooming), and 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) without differences among groups. In Exp. 3, the same goats (IUTN and IUHS; n = 8) used for HS behavior (Exp. 2) were used. Body weight, feed intake, water consumption, RT, RR, and also blood glucose, insulin, NEFA, BHB, cholesterol and triglycerides were measured. Additionally, 4 goats per treatment were subjected to a glucose tolerance test (GTT), insulin tolerance test (ITT), and epinephrine challenge, each one performed once during P1 and P2. Regardless in utero conditions, HS showed increased (P < 0.01) RT, RR and water consumption, but decreased (P < 0.05) BW 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 GTT. In conclusion, LT goats had similar DM intake to TN goats, but greater milk fat and protein. The LT goats covered the extra energy needed for heat production by mobilizing body fat reserves as indicated 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.
