Graduate Thesis Or Dissertation
 

Certain genetic and maternal environmental influences on growth rate and body composition of lambs

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  • The present study was designed to investigate the relationship of milk production and milk quality to growth rate and certain organ-oleptic measurements of lambs of mutton breeds, Nine mature ewes in their fourth lactation of the Border Cheviot, Dorset Horn, Columbia, Suffolk, and Willamette breeds were acquired making a total of 45 ewes. An attempt was made to synchronize parturition, The reason for synchronizing parturition was to have all the ewes lamb during a narrow interval of days so that milk production and its effects on growth could be measured under environmental conditions that were as similar as possible. The ewes were milked by use of oxytocin to cause them to eject the milk in the udder after which they were kept separate from their lambs for six hours and milked again. The milk obtained for the six-hour period was weighed and the quantity recorded. A representative sample was taken from milk of each ewe for composition analyses. The average percentage composition of the milk from ewes was found to be: protein, 5.46; lactose + ash, 5.40; solids-not-fat, 10.86; fat, 8.43, total solids, 19.29; and water, 80.71. There were no significant differences (P >.05) between breeds for the percentage of milk components studied. During the first eight weeks of lactation the breeds studied had produced 74 percent and by ten weeks they had produced 87 percent of the milk yield for the total lactation period. The breeds ranked in the following order on the basis of milk yield and milk quality: Suffolk, Willamette, Dorset Horn, Border Cheviot, and Columbia. The latter two breeds were approximately equal. Ewes nursing twin lambs produced 25 percent more milk than ewes nursing single lambs, The peak of lactation occurred in the third and fourth weeks of lactation, The average grams of milk produced per day for ewes nursing single and twin lambs, respectively, are as follows for the five breeds: Border Cheviot 1, 016, 1, 669; Dorset Horn 1, 617, 1, 778; Columbia 1,366, 1,684; Suffolk 1,527, 2,287; and Willamette 1, 552, 1, 951. A set of twins gained on the average 40.7 percent more than a single lamb. Single lambs gained 15.7 percent rnore weight than the average of a set of twins. The Willamette had the highest average daily gain and was followed in order by the Suffolk, Columbia, Dorset Horn, and Border Cheviot. The average grams of milk consumed for each gram of gain for single and twin lambs, respectively, are as follows; Border Cheviot 3.964, 3.455; Dorset Horn 5.472, 3.424; Columbia 4.406, 3.716; Suffolk 4.326, 3.882; and Willamette 4.193, 3.114. It was concluded that a large portion of the nutrients required for lamb growth and fattening must be supplied by foods other than milk. Highly significant differences among breeds of sheep (P <.01) were found to exist for weaning weight. Weight differences between sexes within a breed were not significant, and there appeared to be no significant interaction between breed and sex. A correlation coefficient of 0.84 between total gain of the lamb and total grams of milk produced by its dam was highly significant. Seventy percent of the variation in total gain is accounted for by variation in total milk yield. The breeds ranked in the following order for carcass tenderness and composite preference of meat; Columbia, Willamette, Dorset Horn, Border Cheviot, and Suffolk. It was postulated that lamb weight at eight to ten weeks of age would be a better criterion by which to cuIl low producing ewes and to select replacement females and males than the 120-day weight. The conformation score, composite preference score, tenderness score, and the percentage of protein, solids-not-fat, milk fat, and total days nursed, were not affected by the breed, sex or rearing of the lambs studied. Only 100-day weight and condition scores were affected by breed. Total gain of the lamb was affected by the quantity of milk and milk components produced by the dam.
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