Abstract:
WATER CONSUMPTION AT PASTURE OF .MERINO SHEEP SELECTED FOR HIGH WOOL PRODUCTION By C. H. S. DOLLING*, and M. T. C Summary ARPENTER * The daily consumption of water at pasture by two groups each of 50 medium Peppin Merino ewes has been measured for a period of 56 days. One group represented a flock in which selection for high clean wool weight per head had raised the two-tooth wool production to a level 20 per cent. higher than that of the control flock, from which the second group was chosen. The average daily water consumption of the selected sheep was 6.7 lb per head, that of the control sheep 6.2 lb per head. The difference of 05 lb was significant at the 5 per cent. level. The mean body weight on pasture of each group fluctuated around 100 lb, which suggests that the rate of water turnover is higher in the selected sheep than in the control sheep. I. INTRODUCTION Selection for high clean wool weight per head over a period of 8 years in a medium Peppin Merino flock at 'Gilruth Plains' has increased two-tooth ewe wool production by 20 per cent. (Turner 1960). The improvement from selection has been measured against ` closed control flock for which all breeding stock a replacements were selected at random. Some of the superiority of the selected sheep has resulted from a higher efficiency of conversion of food into wool (Turner, personal communication; Dolling and Moore 1960). It has been postulated that the remainder of the superiority results from a higher intake of food at pasture. To test this hypothesis, an experiment is in progress to estimate relative pasture intake in the field, groups of sheep being weighed on and off pasture after starvation. The analyses of estimates of relative food intake are not yet available, but observations on daily water consumption were also made and are of interest. II. MATERIALS AND METHOD (a) Sheep and Pasture A group of 50 ewes chosen from the 1957 drop of the selected group was such that its clean woo\ production per head had a mean and variance similar to those of the whole drop. A second group of 50 ewes was chosen from the control group in the same manner. The selected ewes had averaged 4*9 lb clean wool per head at 16 months of age after an 1 l-month growing period; the control ewes 4.1 lb. The ewes were shorn on September 21 and 22, 1961. The two groups of ewes were grazed separately from October 7 to December 13 on Mitchell grass * Division of Animal Genetics, C.S.I.R.O. National Field Station, 'Gilruth Plains, ' Cunnamulla, Queensland. 172 T ABLE 1 \ DAILY MEAN WATER CONSUMPTION PER HEAD OF SELECTED AND CONTROL EWES Date Daily Mean Water Consumption Per Head (lb) Selected Control 9.3 65 8.8 6.1 9.4 4*0 6.6 7.0 4a7 8*8 9*1 5=1 6*0 5.6 4.7 9.0 498 9.7 6.4 7.5 5~8 992 6*8 7*6 395 3.5 6.6 6.5 5.4 Features of Environment .105aot 104.0, 3 point& 27 points Date Nov. 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Dec. 1 2 3 4 5 6 7 8 9 1c 11 12 13 14 Daily Mean Water Consumption Per Head (lb) Selected ' Control Features of Environment off pasture Oct. 14* 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Nov. 1 2 3 4 5 6 7 8 9 10 11 12 13 9.5 7.1 9.0 6.5 9.7 5.3 5*2 996 4.8 8.0 10.6 7.3 5.5 4.9 6.2 9*5 796 7.5 10.8 5.4 698 8.6 5.2 12.0 4.4 4.1 8.0 690 10.2 2 points 7 points off pasture* * 7.0 4*1 0.9 6*4 2.4 8.9 698 8bl 3.9 5.9 5.2 5a7 5.0 994 5.7 5.8 2.9 3*4 996 899 5*6 8.3 4*2 892 6*4 3*1 8.7 690 5*3 l-8 4*4 4*0 790 5.6 7.3 3*7 494 4.9 4.7 5.9 9.0 6.7 3.9 4.2 490 10.6 5.7 596 7.3 5.2 593 8.4 2.5 8.4 28 points 9 points 102.2 102.6 off pasture 12 points 104*4 103.4 off pasture off pasture ' 103 94 107-8 104*5 101.2 13 points 104.2 off pasture 35 points Selected Average * Consumption measured at 7.30 a.m. 6.7 Control 6.2 'f Maximum temperature in 24-hour consumption period where greater than lOOoF. $ Rainfall in 24-hour consumption period. *`$ All ewes were held off pasture but on water .for 24 hours. Water consumption omitted from consideration. 173 pastures, which contained a considerable amount of dry grass and herbage, produced by summer rains commencing in the previous January, but very little green material. The rainfall in points was, September 0, October 81, November 62, and December (until 13th) 0. (b) Water Corwmp tion The two flocks were alternated each morning between two 25-acre paddocks. From October 14 to December 13 the water consumption of each flock during each 24 hours was recorded immediately prior to the changing of paddocks. In each paddock, three iron troughs each 8 feet long were filled daily to a pre-determined level. The total water added (W,) represented the 24-hour change following loss due to drinking by sheep (and possibly by native fauna) and to evaporation, and gain from rain. Outside each paddock, but adjacent to the drinking troughs, a fourth trough was filled daily to the same level. The water added (W,) represented the 24-hour change following loss due to evaporation, and possibly native fauna, and gain from rain. The water consumed by sheep was taken as W, -3W,. III. RESULTS AND DISCUSSION The mean water consumption per head of each group during each 24-hour period is given in Table 1. No figures are available for the consumption by individual sheep, but the average daily mean consumption of the selected ewes was significantly greater than that of the control ewes (paired t test, t,, = 2.46, 0*02 + P > 0.01). Th e selected ewes drank approximately 8 per cent. more water than the control ewes. The water consumed by drinking would not have been greatly below the total water intake of the sheep; their intake of what was a dry pasture was probably not high because the ewes declined in body weight during observations. The mean body weight of each group fluctuated around 100 lb when sheep were weighed immediately off pasture. If the total body water is similar in the two groups, the selected sheep must have a higher turnover rate of water than the control sheep. Ferguson (personal communication) has found a positive correlation between water consumption and food intake of sheep fed under pen conditions. Should this relationship hold in the field, the results presented here suggest that the selected sheep have been consuming a greater amount of food at pasture than the control sheep. It is hoped that the results of the current experiment will indicate whether or not this is SO. IV. ACKNOWLEDGEMENTS It is a pleasure to acknowledge the field assistance of Miss J. Cowell, and the helpful discussions held with Miss H. N. Turner and Mr. M. G. Brooker. V. REFERENCES D OLLING , C. H. S., and M OOR E, R. W. ( 1960). - Efficiency of conversion of food to wool. I. Correlated response to selection for high and low clean wool weight per head. T URNER Aust. J. Agric. Res. 11: 836-844. , HELEN N EWTON ( 1960) .-Selection to improve flocks and herds. Farmers ' and Scientists' Joint Conference, 1960 (Australian Institute of Agricultural Science and Farmers' Union of Western Australia: Perth). 174