Concept of multiple environmental stresses impacting sheep production and adaptation under the changing climate scenario

Background: Climate change is a major threat to the viability and sustainability of livestock production systems in many regions of the world. A considerable population of poor people depends on animals for food, fibre, income, social status, security, and companionship. Hence one of biggest challenges facing animal science currently is to increase the production in the context of climate change. Animals reared in tropical environments are generally subjected to more than one stress at a time. This greatly influences the animal production and reproduction under such environmental conditions. Nearly all studies on the effect of environmental stress on farm animal productivity have generally implicated one stress at a time since comprehensive, balanced multifactorial experiments are technically difficult to manage, analyze, and interpret.

Hypothesis and Objectives: The hypothesis of the present study is that multiple stresses effecting livestock productivity is a common phenomenon due to climate change under semi arid tropical environment and this has much profound impact on livestock production than temperature stress alone. With this intention, the proposed study has been undertaken with the primary objective to establish the effect of multiple stresses (thermal, nutritional and walking stress) on physiological response, blood biochemical and endocrine responses in Malpura ewes.

Methodology: Two experiments were conducted to satisfy the objectives. The study was conducted for a period of 35 days covering two estrous cycles under controlled conditions. Twenty-eight adult Malpura non-pregnant ewes were used in the present study. The ewes were randomly allocated into four groups of seven animals each viz., GI (n=7; Control), GII (n=7; thermal stress), GIII (n=7; nutritional stress) and GIV (n=7; combined stress). In the second experiment, the Malpura ewes were randomly allocated into two groups of twelve animals each viz., GI (n=12; Control) and GII (n=12; Multiple stresses). The animals were stall fed with a diet consisting of 60% roughage and 40 % concentrate (barley, 650 g/kg, groundnut cake, 320 g/kg, minerals 30 g/kg including 10 g/kg NaCl, with crude protein = 180 g/kg and total digestible nutrients = 650 g/kg). GI and GII ewes were provided with ad libitum feeding while GIII and GIV ewes were provided with restricted feed (30% of intake of GI ewes) to induce nutritional stress. Further, the multiple stress group ewes were subjected to walking stress by forcing them to walk for 14km. This 14Km was covered in two spans. The animals took one hour and 30 minutes to complete one span (7KM) and accordingly the first span was between 9:00 h to 10:30 h and the second span between 15:00 h to 16:30 h. Physiological responses and body weight measurements were recorded at weekly interval. Blood collection was done at weekly interval and plasma was separated for estimating the biochemical and endocrine parameters. The parameters studied were: body weight, respiration rate, pulse rate, rectal temperature, plasma glucose, total protein, total cholesterol, cortisol, thyroxine, tri-iodo-thyronine, estradiol, and progesterone. Data generated were analyzed using multivariate analysis for repeated measurements.

Combined Stress: The results from the first experiment indicated that combined stress (heat and nutritional stress) significantly (P < 0.05) reduced body weight, estrus duration, conception rate, lambing rate, birth weight of lambs, and estradiol 17-β while significantly (P<0.05) increased estrus cycle length and progesterone. Further, combined stress significantly (P<0.05) affected the feed intake, water intake, respiration rate and rectal temperature. In addition, in relation to thermal stress, restricted feeding had less significant effect on the growth and reproductive hormone levels in the ewes. However, when both these stresses were coupled, it had severe effect on growth and hormone parameters studied in these ewes. Results from the second experiment showed that multiple stresses (heat, nutritional and walking stress) significantly (P<0.05) affected body weight, estrus %, estrus duration, conception rate, lambing rate, respiration rate, pulse rate, rectal temperature, sweating rate, tri-iodo-thyronine, thyroxine, cortisol, estradiol, progesterone haemoglobin, packed cell volume, glucose and total protein. Compared to single and two stresses (heat and nutritional stress) simultaneously in previous studies, multiple stresses in the present study had much higher detrimental effects on most of the parameters studied. When walking stress is coupled with heat and nutritional stress, it had severe impact on all the parameters studied in these ewes. As these are the first detailed studies which report effect of multiple stresses in domestic livestock, the findings have greater significance in terms of understanding the ideal requirement for these animals to adapt to tropical environment without compromising production.

Conclusion: The studies clearly establish the severe impact of multiple stresses on biological functions, necessary to cope with these stresses, in Malpura ewes. This is evident from the significant differences in majority of the parameters studied in multiple stresses group. Further, the study indicates that Malpura ewes have the capability to adjust their physio-biochemical responses to cope with multiple stresses under hot-semi arid environment. The findings from the study have higher significance since it's not only the heat stress that is causing severe damage to livestock productivity but also the multiple stresses which occur simultaneously as result of changing climatic conditions. Hence its very pertinent to conclude from these studies that when two or more stressors occur simultaneously, they may have severe impact on biological functions necessary to maintain homeostasis in sheep.

Future Perspectives: Multiple stresses are a common phenomenon under semi arid tropical environment due to climate change. Any research pertaining to climate change effect on livestock production must address these multiple stresses simultaneously in future. These types of investigations will be instrumental in gaining a thorough understanding of the exact requirements in mitigating the adverse effects of environmental stress simultaneously on sheep production.