Productive performance of crossbred cows in hot humid environment

Abstract

The physiological and productive adaptability of Brown Swiss, Holstein Friesian Jersey crossbreds in hot humid environmental conditions of Kerala was evaluated. Effect of dietary supplementation of buffer salt and feeding of high proportion of undegradable protein to ameliorate the effect of stress also studied. Variuos biochemical parameters in blood and milk were screened for identifying biological markers of adaptation. The relevant literature had been reviewed. The major stress factors for cattle had been enumerated. The heat stress in particular was dealt with exhaustively and its impact on crossbred dairy cattle organized under physiological, lactational, hormonal, reproductive, nutritional and metabolic responses. The role of physiological modification of the environment, genetic development of heat resistant breeds and various nutritional strategies which had been adapted for amelioration of heat stress also reviewed. The experimental schedule comprised of three trial periods. The Trial I was designed to study the macrolevel responses due to added climatic stress while Trial II was to evaluate two stress ameliorative treatments viz. dietary supplementation of buffer salt (sodium bicarbonate at 0.85 percent of concentrate ration) and partial substitution of dietary protein with protein of low degradability. Trial III was mainly aimed at understanding the more intrinsic and subtle microlevel changes of the adaptive process. The protocol for the experiment followed was essentially the same for all the three trials. For Trial I, eight crossbred cows from three genetic groups were exposed to direct solar radiation from 9 AM to 3 PM, while equal number of animals were kept within the shed throughout the day. Except for the exposure, feeding and other managemental conditions remained same. Milk and blood samples were collected immediately after the exposure period (3 PM) from exposed and sheltered animals once in four days. A total number of six samples were collected during the trial period. Physiological responses were measured daily before and after the exposure period. Recording of climatic variables were done using approved instruments and methods. Milk samples were analysed for total solids, fat, solids- not – fats, whey protein, calcium, magnesium, sodium, and potassium. During Trial II period, half the number of animals of each genetic group was fed supplementary buffer salt and undegradable protein. The parameters studied were same as that of Trial I. In Trial III, a fresh set of animals were used and the parameters studied were different. The blood constituents estimated were lactate dehydrogenase (lDH), glutamic oxalacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), triiodothyronine (T3) and thyroxine (T4). Milk samples were not analysed during Trial III as in the previous two trials. Climatic indices and adaptive indices were computed, means and standard error of milk and blood constituents as well as physiological responses were worked out, statistical significance tested, correlation and multiple regression coefficients worked out and presented in Tabels I to 50 and the results illustrated using Figures I to 10. Sophisticated analytical procedures like atomic absorption spectrophotometry, automatic enzyme analysis and radioimmuno assay techniques were employed apart from the other standard methods used. From the results obtained, the adaptive indices based on physiological responses appeared to have failed in. ranking the genotypes in terms of their relative adaptive ability to hot humid conditions. The inbuilt drawbacks of the adaptive indices based on physiological responses were discussed, as well as, questioned the desirability of having a narrow range of physiological responses in an adaptive index. Dietary supplementation of buffer d=salt and feeding of undegradable protein had helped in ameliorating the effects of heat stress in cattle. The beneficial effects of the treatments were more for high stressed than in low stressed cows. The results of Trial III regarding the physiological parameters and adaptive indices showed similar trends as that of Trial I. One important observation was that the levels of triiodothyronine (T3) levels differed significantly between exposed and sheltered animals, the exposed had low levels compared to sheltered counterparts. To be able to produce well in hot humid environments, whatever be the strategies an animal adopt with minimum effect on productive processes, due recognition need be given. If high respiratory frequency is a necessary strategy, it should be taken as a positive attribute. Supplementation of buffer salt at 0.85 percent of the concentrate ration can be advocated for stress amelioration. The possibility of incorporating blood levels of triidothyronine in adaptive indices with productive parameters need to be explored. There is also scope for improving the efficiency of adaptive indices, now in vogue, by providing due weightage for the attribute of having low basal physiological response levels combined with the rate of decline in milk production, under high heat stress conditions.