Abstract:
MILK PRODUCTION AND CALF GROWTH RATE IN HEREFORD, AFRICANDER-SHORTHORN AND BRAHMAN-SHORTHORN CATTLE IN QUEENSLAND J. H. G. HOLMES,* A. TAKKEN* AND G. W. SEIFERT Summary The daily -milk production of 67 Hereford cows at the C.S.I.R.O. Pasture Research Station, Samford, near Brisbane, and of 24 F1 Africander-Shorthorn and 19 F1 Brahman-Shorthorn cows at the National Cattle Breeding Station 'Belmont', near Rockhampton, was estimated at monthly intervals during summer and autumn by measuring the amount of milk secreted in 6 hr. intervals between injections of oxytocin. At Samford, there were positive correlations between estimated daily milk production and calf growth in successive months of 0.66, 0.66, 0.57, 0.30 and 0.67. The correlation of total milk production with calf growth rate to six months was 0.82. At 'Belmont' there was a similar relationship between estimated daily milk production and calf growth rate. Lactation curves of the crossbred cattle were more varied and their milk yields were significantly higher than those of the Herefords at Samford. The Africander crossbreds had higher initial `milk yield than the Brahman crossbreds, but declined in yield more rapidly. I. INTRODUCTION Experiments in Queensland (Lampkin and Kennedy 1965 ) and Florida (Peacock et al. 1960) showed that Brahman-Shorthorn cross calves grew more rapidly to weaning than purebred calves under the same conditions. Improvement in the growth rate to weaning of the F2 crossbred calves measured by Lampkin and Kennedy ( 1965) might be due to heterosis in the calf or to increased milk production by the Fl crossbred dam. Gifford ( 1949) measured the milk production of 57 Hereford cows and found the daily yield fell from 3.9 to I 1.9 kg over the first eight months of lactation. Correlations between milk yield and monthly calf growth ranged from 0.7 to 0.5 for the first three months, but were not significant thereafter. Heyns ( 1960 a, b) observed similar correlations with pure-bred Africanders and Neville ( 1962) in Herefords. Milk yield and calf growth of cattle in Queensland were estimated by Arbuckle ( 1959), Ryley (1961), Stubbs (1962) and Bewg ( 1967). There is much information on the milk production of Zebu types of cattle, mainly dairy breeds (Mahadevan 1966). A study of the measurements of milk secretion rate by oxytocin injection (Lamond, Holmes and Haydock, unpublished data) has been applied to the estimation of the milk production of Hereford and Fl Bos indicus x B. taurus cows. The yield and composition of milk were estimated monthly, and relationships with calf growth were examined. 'C.S.I.R.O., Division of Animal Physiology, Cunningham Laboratory, Brisbane. tC.S.T.R.O., Division of Animal Genetics, National Cattle Breeding Station, Rockhampton. 163 II. MATERIALS AND METHODS (a) Animals and Management Sixtykseven Hereford cows, aged from 3-10 years and mated with Hereford bulls, calved between Oct,ober 7 and November 30, 1964 and were grazed at the C.S.I.R.O. Pasture Research Station, Samford, on a wide range' of subtropical legumes and grasses of generally good quality. The milk production of all COWS which had calved more than nine days was measured and their calves were weighed at four week intervals from November 11, 1964. Early -born calves were weaned on March 30 and late born calves on April 22, 1965. Nineteen Brahman x Shorthorn (Fl ) cows and 24 Africander x Shorthorn (Fl ) cows mated with corresponding Fl bulls were grazed as one herd on native pasture, predominantly Heteropogon contortus, at the National Cattle Breeding Station, 'Belmont', 15 miles (24 km) north of Rockhampton. The animals, pasture and breeding programme were described by Kennedy and Turner ( 1959). The production of cows which had calved more than seven days was measured and their calves were weighed at four week intervals from October 23, 1964. Calves were weaned on May 17, 1965. On the days when production was to be measured, the calves were separated from the cows at 0700 h and held in a yard. Oxytocin*, 20 i.u. in 2 ml saline, was injected into the jugular vein of the cow, teat cannulae were inserted and the udder was drained. After grazing for about 6 h, the cows were again yarded and the udder was emptied in the same way. Milk secreted in the interval, timed to 1 min from injection to injection, was recorded and sampled, and the 24 h yield was calculated pro rata. Daily milk production during each month was taken as the mean of the yields measured at the beginning and the end of the month. Usually 25-30 cows were milked in a day. Milk fat was determined by the Te-Sa detergent method (A.O.A.C. 1960). Solids-not-fat (SNF) was calculated from the density of the milk and its fat content (British Standards Institute 1960). Gross energy of the milk (E, kcal) was calculated by the formula: where the milk yield and fat are in g, SNF is a percentage, and the value of 0.7 was adopted as a general mean ash content. Protein was calculated from the equation, derived from data of Turner (1936) : (c) AnalyticaL (b) Milking procedure III.. RESULTS Milk yields and composition are given in Table 1, correlations with calf growth in Table 2 and regressions of calf weight gain on milk yield in Table 3 Mean values are shown in Figure 1 a. *Oxytocin - Posterior. pituitary extract - Crookes Ltd. 164 (a) Herefords 165. TABLE 2 The number of cows studied declined during the experiment because some calves died. Some late-born calves were weaned before day 136 or 164 of lactation. Correlations between calf weight-gain and estimated milk yield were uniformly high except in month. 4, and the individual records giving the lactation curves shown in Figure la were regular and free from anomalies. The lactation curves show an initial yield of about 7 kg decreasing steadily to about 3 kg at 160 days. (b > Crossbreds Estimates of` the yield and composition of milk are given in Table 4; calf weights and mean milk yields are graphed in Figure lb. Some of the Brahman-cross calves were not weighed at weaning and thus only nine cow-calf pairs were available for the calculation of correlations between calf growth-rate to weaning and milk production. The correlations over the period 0 to 4 months were, r = 0.78 (P < 0.01 ), for the Brahman cross and r = 0.46 (P < 0.05) for the Africander cross; for the period from birth to weaning they were 0.60 (P < 0.01) and 0.70 (P < 0.001) respectively. The correlation of calf weight gain from 80 to 120 days with corresponding milk production was 0.7 1 (P < 0.01) for each breed. Correlations were not calculated for individual months. The Brahman cross cows were more excitable than the Africander cross or the Herefords, and accurate milk collection was sometimes difficult. Some secretion rates measured were erratic: one cow gave estimated yields in successive tests of 10, 6, 13, 7, 3 kg and another 10, 8, 15, 8, 7 kg. Regression analysis of the individual curves showed that 20 of the 24 Africander crosses had significant decreases in production over the 4-month period; the average withincow regression of yield on time was highly significant and had a coefficient of TABLE 3 167 TABLE 4 Yield atnd Composition of milk of Brahman crow and Africander cross cows at Belmont. - 0.040 kg/day. The Brahman cross were more variable and mar& .:. did ., cows not show a' significant fall in milk yield over 120 days. The average within-cow regression was significant (P < 0.05) and had a coefficient of - 0.014 kg/day. There was little difference between breeds . in the composition of the milk. IV. DISCUSSION ,.. (a) Herefords In the Hereford herd at Sainford, the oxytocin method gave estimates of milk yield which were consistently related to calf growth with correlation coefficients similar to:.. those reported by Gifford ( 1949), Neville ( 1962) and Heyns (1960 a, b) The daily milk yields were somewhat higher than those o the Hereford-Shorthorn cross cows of Arbuckle (1959) but comparable to those reported for Shorthorn and Hereford cows by Drewry, Brown and Honea ( 1959), Dawson, Cook and Knapp (1960), Gifford (1949). and Neville (1962), all of whom used calf-weighing methods of estimating yield. The reciprocals of the regression coefficients of calf weight gain on milk syield (Table 3) indicate that the weight of milk consumed per unit weight gain from birth to weaning was about 15 units. This is intermediate among values reported by Neville ( 1962) and Drewry, Brown and Honea ( 1959). The high regression coefficient, 0.132, in the period 136-l 64 days (Table 3 ) is thought to be the result of a period of 168 169 dry weather which depressed milk yield more severely than it affected calf growth rate. The lower correlation (0.32) in this period (Table 2) is a further indication of this. The fat content of the milk, 4.1 to 5.1%, was appreciably higher than the 3 to 4% reported by Giff ord ( 1949) and Dawson, Cook and Knapp ( 1960). It seems reasonable to conclude that the method used, which was similar to that used by Antony et aZ. (1959)) gave valid estimates of the milk production of the Herefords and that the results accurately described their performance on good pastures in a subtropical climate. Considerable difficulty was experienced in injecting, and collecting milk from some of the Brahman cross cows, and it is not unusual for Brahman cattle to be troublesome under unaccustomed handling. The variability thus produced in successive estimates of milk yield in several cows was largely an artefact, and for this reason observations from five cows with widely inconsistent milk yields were excluded from the analysis. The remaining data showed close correlations between calf growth rate and milk- yields, and the yields were comparable to those obtained by Heyns (1960 a, b) from pure-bred Africander cows. Fat contents in the present work were similar for the two crosses and ranged from 4.2 to 5.0% . This is appreciably higher than the value of 2.82% observed by Heyns ( 1960 a) and suggests, as Heyns pointed out, that his method of milking one side of the udder while the calf sucked the other, may not have given a completely representative milk sample. The growth rates of Heyns' calves were generally higher than those observed here. The higher growth rate of our F2 Brahman cross calves (0.9 kg/day) than of the F2 Africanders (0.8 kg/day) is consistent with the better sustained lactation of the Fl Brahman cross COWS. These arguments all suggest that the present oxytocin method gave valid estimates of milk yield for most of these cattle. Future work with B. indicus or crossbred cattle would clearly require care in the training and handling of the cows and the design of yards and equipment to facilitate the work. *No rigorous comparison of the crossbred with the Hereford cattle is possible because of the confounding of breed with environment in this work, but the improved pastures at Samford would probably provide better nutrition than those grazed at Belmont. Despite this, the Herefords produced significantly less milk than both crossbred groups. Their calves, 34 kg at birth, were intermediate in weight between the F2 Africanders (35 `kg) and the F2 Brahmans (32 kg) but grew at a slower rate, averaging 0.6 kg/day from birth to 200 days, compared with 0.9 and 0.8 kg/day for F2 Brahmans and F2 Africanders respectively. These values are similar to those reported by Stubbs ( 1962). Heyns ( 1960 b) noted an increase towards the end of lactation in the values of the correlation and regression coefficients for calf weight and milk production; he also found that calves born late in the season received less milk, grew more slowly, and the correlation of growth with milk production was higher than that of the early calves, for which better grazing was available. A similar conclusion is suggested by the high correlation here in the Africander cross between calf growth and milk production, from 80 to 120 days. 170 (b) Crossbreds (c) General It appears likely that the initial milk production was so high that variation in yield was not of great importance since milk availability was not limiting calf growth. Heyns ( 1960 b,) demonstrated a high correlation (r = 0.79) between birth weight and capacity to consume' milk and between birth weight and total milk . production, and confirmed Gifford's ( 1949) observation that the young calf might be unable to consume all the milk available, and that production might in consequence be reduced. As the calf grows, its ability to consume milk increases as the amount of milk available decreases and, as will often occur, pasture quality deteriorates. Protein content of pasture may fall to as low as 2% in the dry matter - in typical dry season pastures (Kennedy and Turner (1959). If the degree of correlation of growth rate with milk production is a true reflection of the calf's dependence on milk, the milk yield may be as important at 6 months as at 1 or 2 months, according to the grazing available to the calf. V. ACKNOWLEDGMENTS This work was part of a programme initiated by the late Dr. M. C. Franklin and Dr. D. R. Lamond to determine milk production of grazing beef cows in relation to calf performance. We wish to express our thanks to Dr. J. GrifEith Davies, Chief of Division of Tropical Pastures, and to Mr. J. Kennedy, Officerin-charge, 'Belmont', for allowing us access to their cattle and for providing assistance. The contribution of the Division of Animal Physiology was supported by funds from the Australian Meat Research Committee. VI. REFERENCES ANTONY, A.O.A.C. ( 1960). 'Official Methods of Analysis'. 9th of Official Agricultural Chemists. ARBUCKLE, J. ( 1959). Q d agric. J. 85: 173. B EWG, W. P. (1967). Tropical Grasslands. 1: 72. 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