Thermal, Haematological and Lactational Responses of Grade Dairy Cows

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Hamid Ragab, Hamid
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This study was conducted on 9 cows from the dairy herd of the University of Khartoum Experimental Farm. The animals were grouped into three equal groups to investigate the effect of the level of exotic blood (50% and <50% Friesian inheritance) as well as the stage of lactation on thermal, haematological, lactational and luteal responses of grade dairy cows. The level of Friesian inheritance did not significantly affect the rectal temperatures (Tr) of the cows. However, low grade cows (<50% Friesian blood) were more heat tolerant than high grade cows (50% Friesian blood). The regression analysis indicated that Tr of the cows decreased as the ambient temperature (Ta) increased. High grade cows maintained higher plasma metabolites and lower packed cell volume (PCV) and thyroid hormone levels (thyroxine, T4 and triiodothreonine, T3) than the low grade cows. However, the difference between the two groups was significant only for T4 (P< 0.05). All the studied traits were affected by the advance of lactation (time) except the plasma total proteins (P< 0.0l) for cholesterol and T4 (P< 0.00l) for PCV, glucose and T3. The high prevailing Ta during the experiment contributed to these changes. Level of Friesian blood x time interaction was significant for PCV, T3 (P<0.00l) and T4 (P<0.0l). However, only, the milk yield was significantly affected by the level of Friesian blood (P<0.05). The milk yield and protein content of the milk were significantly affected by the advance of lactation (time) (P<0.0l and P<0.00l for the two traits, respectively). The interaction between the level of exotic blood and time was significant for milk yield (P<0.0l), milk protein (P<0.05) and milk ash (P<0.00l). High grade cows in early lactation maintained higher Tr than high grade cows in mid lactation (P<0.00l). Regression analysis showed that cows in early lactation were less heat tolerant than cows in mid lactation. There was a negative, non-significant correlation between Tr of the cows and Ta during the experiment. The stage of lactation did not significantly affect any of the studied plasma metabolites and hormones. However, PCV, plasma glucose, T4 and T3 levels were slightly lower in cows in early lactation than in cows in mid lactation whereas there was no difference in plasma cholesterol. There was an increasing trend in all traits in both groups of cows (P<0.05, for total proteins; P<0.0l, for PCV, cholesterol and T4 P<0.00l, for glucose and T3). The stage of lactation x time interaction was significant for T4 (P<0.0l) and T3 (P<0.00l). The stage of lactation significantly affected the milk yield (P<0.05) and milk ash (P<0.00l) of the high grade cows. Of the measured traits, milk yield, protein and ash were significantly affected by time (P<0.00l). Stage of actuation x time interaction was significant only for ash (P<0.00l). The higher milk yield of the high grade cows compared to the low grade cows despite their lower heat tolerance indicates their suitability for dairying in Khartoum. Higher plasma metabolites accompanied by lower plasma T4 and T3 and lower lacteal yield can be used as indices for selection for higher milk production under the climatic conditions of Northern Sudan.
Thermal, Haematological,Lactational Responses,Grade Dairy Cows