Comparative slaughter was used to assess the effects of body-weight loss on Brahman cross (BX) and Africander cross (AX) steers of the F 3 generation with respect to gross dissected carcass composition and the distribution of these components over the dressed carcass. Animals were slaughtered at design body weights of 325, 341, 358, 374 and 390 kg, some while during positive body-weight growth (Group A), and others during weight loss from 390 kg at a rate of approximately 0-5 kg/day (Group B).Gross composition was similar in the two breeds, irrespective of the body-weight loss treatment. Body-weight loss resulted in muscle and fat approximately reversing the path of development, while bone and fascia and tendon remained approximately constant. No evidence of proportionally early loss of fat and later loss of muscle was found. Of the fat components, kidney and channel fat showed the highest relative loss.The distribution of muscle was different between the breeds, the most statistically significant differences being that AX had heavier muscles around the spinal column and lighter shin muscles, at the same total muscle weight. Bone weight distribution differences also occurred, with AX tending to have lighter leg bones, at the same total bono weight. A breed difference in intermuscular fat distribution meant that the AX animals were earlier developing in the forequarter and later developing in the hind quarter in respect to its intermuscular fat, than the BX animals.Body-weight loss affected muscle-weight distribution, the most marked effect being that the relative proportion of abdominal muscles fell during body-weight loss. Boneweight distribution was affected to a minor extent, the effects mainly being in the leg bones rather than the axial skeleton. The distribution of neither fascia and tendons nor subcutaneous fat was affected by the body-weight loss treatment, but the distribution of intermuscular fat was affected.
This experiment was designed to measure the effects of infestation by B. microplus on cattle and to separate the effects of reduced food intake ("anorectic effect") from those due to the remaining factors of tick infestation ("specific effect"). Hereford cattle kept on a high-quality diet were studied over a treatment period of 11 weeks with the tick-infested animals being infested regularly with equal larval doses for each animal.The anorectic effect accounted for approximately 65% of the depression of body weight due to tick infestation. Body weights were not related to the numbers of maturing female ticks counted on the infested animals. However, the body weights were related to food intake, the large variation in which was considered a reflection of the variable effect of the toxic principle of the tick on the appetite of the cattle.After treatment, tick-infested cattle were kept clear of tick and run with the two control groups of cattle. Pasture was supplemented with extra rations. The compensatory gain made by the infested group was less than that of the group which had been matched with it for food intake and kept tick-free. This indicates a severe effect on the metabolism of the tick-infested animals, with prolonged after-effects.
This paper describes part of an investigation of the effects of developmental growth and body weight loss on the carcass composition of Angus steers. A method of anatomical dissection was used on one half (the right side) of each carcass to find the weights of each carcass component. The results are compared with those obtained from a method of dissecting butcher's joints used on the other (left) half of each carcass. Two groups of steers were used in this experiment: group A, which grew continuously, and group B, which grew like group A and were then subjected to a period of weight loss before slaughter. Corresponding animals in both groups were killed at the same body weights. Statistical analysis was by analyses of covariance of weights of components converted to logarithms. As carcass weight increased, the proportions of muscle, bone, and fascia and tendons decreased, while the proportions of the fat components increased. This result was similar to that obtained. previously by joint dissection, but the changes differed in degree. Distribution of muscle and bone changed significantly as the total weights of these components increased. Distribution of the other components was known only in so far as they came from either the hindquarter or the forequarter; no changes were found in their distribution as their total weights increased. Comparison of group A and group B animals at the same carcass weight showed that body weight loss led to a significant increase in the proportion of bone in the carcass but only a slight decrease in the proportion of muscle. Body weight loss had a differential effect on the proportion of kidney and channel fat in the carcass, the result depending on the weight at which animals were killed. The weight of subcutaneous and intermuscular fat in the group B carcasses did not vary significantly from that of group A carcasses of the same weight. These results were similar to those found by joint dissection but there were differences in magnitude. In particular, the differences in muscle weight between group A and group B carcasses was more pronounced in the joint dissection, where it was statistically significant. Also bone weight from the joint dissection was affected differentially by the weight loss treatment at the different killing weights; however, there was no evidence of a differential effect on bone weight in the anatomical dissection. These differences were ascribed to more accurate separation of tissues in the joint dissection. Distributions of muscle, bone, and fascia and tendon were affected by loss of body weight. Unlike joint dissection, anatomical dissection did not show significant effects on the distribution of subcutaneous fat and intermuscular fat due to the weight loss treatment; these differences between results are ascribed to differences between the units used for assessing these distributions.
At the age of approximately 11 months, 19 Angus steers were allotted to two experimental groups, namely, 10 to group A and 9 to group B. Group A animals were grown in pens and fed ad libitum. They were killed, two at each of the following of body weights: 250, 281, 316, 356, 400 kg. Group B animals were grown under similar conditions and killed at the same body weights as corresponding animals in group A; however, they were grown to weights 15% above their killing weights (growing-on phase) and then made to lose weight at 0.5 kg per day by restricting food intake until they reached their planned killing weights (weight loss phase). Huxley's (1932) allometric equation was used in logarithmic form as the basis for covariance analyses of the data. Empty body weight (EBW) increased as a proportion of full body weight as full body weight increased. EBW was higher in group A animals than in group B animals at the same full body weight, reflecting differences in weight of contents of the digestive tract. Dressed carcass weight increased as a proportion of EBW as EBW increased. Dressed carcass weight was higher in group B animals than in group A animals at the same EBW, indicating that the increase in carcass weight that occurred during the growing-on phase was not completely lost during the weight loss phase. During developmental growth, the weights of hide, feet, head, liver, gall bladder, heart, lungs, kidneys, and gut tissue decreased as proportions of EBW. The weight of abdominal fat increased as a proportion of EBW, while the weights of tail, spleen, and blood did not change significantly as proportions of EBW. During body weight loss, the weights of the feet, head, and tail remained close to the weights they had reached at the end of the growing-on phase, although, with the head, this varied considerably with the size of the animal before undergoing body weight loss. All other components lost weight during the weight loss phase. The hide, heart, lungs, and abdominal fat all reversed, approximately, the pattern of development that occurred during body weight growth. The liver, gall bladder, kidneys, gut tissue, spleen, blood, and thymus gland all lost more weight during the weight loss phase than they put on during the growing-on phase. With the liver, kidneys, and gut tissue, the proportion of weight lost varied according to the size of the animal before undergoing body weight loss.
Results of matings made in the Belmont breeding programme from 1954 to 1968 have been analysed. The analysis has been made within three groups. (1) The foundation cows in the years 1954-9; (2) the F x generation which were mated within line in the years 1957-62; (3) the F 2 and F 3 generations which were mated within Africander cross (AX), Brahman cross (BX) and Shorthorn-Hereford (SH) lines in the years 1960-8. Fertility was based on the number of calves born, whether alive or dead, to the number of cows mated.In the foundation cows, Hereford cows had a fertility 9 % higher than the Shorthorns. The difference between the bull breeds was not significant although the mean for the Brahman bulls was 16 % below the mean of the other three breeds. There was a large variation in the fertility of the Brahman bulls. The fertility of the Shorthorn cows was depressed (by 8 %) in the lactating cows as compared with dry cows, while there was an opposite effect in the Herefords. These latter effects showed year to year variation.In the F x generation the differences between the breeds were not significant although both the AX (76-4%) and the BX (81-2%) were more fertile than the SH (70-1%). Estimates of heterosis in the F x generation were 42 % for the AX, 43 % for the BX and 12 % for the SH. Lactating cows were 7 % more fertile than non-lactating cows. There were significant differences between the BX bulls used but not between bulls of the other two breeds. The effect of sires within breed on fertility of daughters was significant only within the SH, and the heritabilities of fortuity were estimated from the variance components for sires within breed to be 9 %, 14 % and 22 % for AX, BX and SH respectively.In the F% and F 3 data the breeds were significantly different in fertility with averages of 77 %, 61 % and 67 % for AX, BX and SH respectively. Thus by comparison with the fertilities of the F x cows no loss of heterosis for fertility occurred in the AX, a very marked loss in the BX and only a slight loss in the SH. A significant interaction between age of cow and lactational status showed that in the mature cows, wet cows had a higher fertility than dry, while the converse applied in the 3-year-old cows. The interaction of lactational status with breed consisted of the wet zebu cross cattle having a relatively low fertility while the wet British cattle had a relatively high fertility. There were significant differences between bulls within each of the three breeds. The effect of sires was significant in the BX and SH. Heritabilities estimated from between sires within breeds variance components were -12 %, 22 % and 25 % for the AX, BX and SH respectively. T . T __ ___._,_,_ _. T Boophilus microplus. While efficiency of production depends on many factors, such as maintenance Zebu and zebu-cross cattle are becoming more requirement and voluntary food intake, the net and more plentiful in the tropical and subtropical reproduction rate can be particularly important areas of Australia. Their use is dependent on their in breed...
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