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    Comparison of milking characteristics and feed conversion efficiency of two lines of Holstein-Friesian cows which differ genetically in live weight : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Dairy Production at Massey University, Palmerston North, New Zealand
    (Massey University, 2002) Tolosa Alvarez, Maria Ximena
    Milking characteristics during peak yield in two consecutive lactations (seasons 2000 and 2001, experiment one); daily milk production and composition, somatic cell count, live weight and body condition score during a complete lactation (2000 season, experiment two); and metabolisable energy intake and feed conversion efficiency during peak lactation (1999 season, experiment three) were studied in three experiments with grazing Holstein-Friesian cows from two selection lines, which differed genetically for live weight. Experiment one (a & b): the heavy line yielded more milk at each milking than the light line but this difference was not significant for any season. Average flow rates were similar for both lines in both lactations (~2.0 litres/min for both lines). Maximum flow rates did not differ between lines either (~3.2 litres/min for both lines). Consequently, total milking times were similar for both lines in both lactations (7.5 vs. 7.3 min and 7.6 vs. 7.8 min for the heavy and the light line for seasons 2000 and 2001 respectively). Experiment two: Cows from the heavy and the light line yielded 22.2 and 20.6 litres/day respectively (p<0.01). Fat yield was similar for both lines because the milk from the light cows had a higher fat concentration than milk from the heavy (4.8 vs. 5.0%; p<0.05). The heavy line yielded more milk protein than the light line (0.8 vs. 0.7 kg/day; p<0.05), however, there were no significant differences between lines for protein concentration. Log transformed milk somatic cell counts were slightly lower for the heavy line both in peak lactation and during the whole lactation, however, this difference was significant only during peak lactation in 2001 (10.8 vs. 11.4x103 cells/ml of milk, p<0.001; and 10.3 vs. 10.8x103 cells/ml of milk, p<0.05 for the heavy and light line for period one and two respectively). Differences in live weight between the heavy and the light line were significant (517 vs. 474 kg for the heavy and the light line respectively; p<0.001). Body condition score during the whole lactation was similar for both lines (4.2). Experiment three: metabolisable energy intake and feed conversion efficiency in peak lactation were similar for both lines (158 vs. 161 MJ ME/cow/day and 108 vs. 106 g MS/kg DM intake for the heavy and the light line respectively). The regression coefficient of metabolisable energy intake on metabolic live weight was 0.65 MJME/kg LW0.75 for both lines. In summary, selection for cow live weight affected the live weight of the cows, had no effect on milk production, and in contrast with other experiments, had no effect on individual pasture intake either per cow or per kg of metabolic live weight nor on energy requirements for maintenance. Finally, selection for cow live weight did not have a consistent effect on milking characteristics or milk somatic cell counts.
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    Measurement, mathematics, and mechanisms of mammalian growth : a thesis presented in partial fulment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1978) Clark, Ross Graham
    Longitudinal growth experiments using rats, lambs, and heifers were analysed by establishing linear relationships between ages, live weights and body lengths in individual animals. Various analytical methods were investigated. Statistical and biological reasons forced the logarithmic transformation of weights and lengths, a three parameter logarithmic metameter was used if means and standard deviations were correlated on a two parameter logarithmic metameter. Age was transformed to give linear relationships. Changes to the experimental design and analysis of growth experiments were suggested. Effects were demonstrated in individual animals that were previously only shown for grouped data and the techniques' sensitivity produced novel findings. Rats were ovariectomised at three ages and/or treated with oestrogen and slaughtered at four ages. The rat ovary inhibited growth pre-pubertally, and the response to ovariectomy or oestrogen was negatively related to the pre-treatment growth rate. Compensatory growth occurred following weaning in rats and following birth in ruminants. Estimated initial weights explained more of the variation in subsequent growth rates than did observed weights. In rats pre-weaning growth lines diverged (compensation being negligible), birth and weaning weights being positively correlated, post-weaning growth rate was strongly negatively correlated with weaning weight. Estimated birth and final weights, and weaning and final weights, were unrelated; compensation being nearly complete. Two sets of pre-weaning lamb live weights (collected by others) were, for individual animals, linearised. Pre-weaning compensation occurred, as it did in two independent sets of weighings from monozygotic twin heifers (also collected by others). Compensatory growth, between and within sets of twin, occurred rapidly to weaning, then slowed. The efficiency of identical twins for experimentation, using these methods, was shown, as were the disadvantages of using average daily gains. The linear relationships did not explain all the systematic variation, short- and long-term oscillations in growth rate occurred. Long-term oscillations were related to live weight rather than to age. Neo-natal testosterone treatment of female rats transposed and advanced the pattern of growth. Both Sex and Strain affected the pattern of growth. The possible use of these techniques in animal breeding was discussed. The logarithms of lengths and weights, assumed by many biologists to be linearly related (allometry), showed curvilinear relationships. A technique of carcass analysis was developed and applied. Ovariectomy increased rat body weight and length but did not produce obesity (assayed by percentage composition and by allometry). Oestrogen stimulated fat deposition but inhibited linear growth. Body weight's response to oestrogen was adaptive,bone growth's non-adaptive. Similarly there was a large pre-pubertal sex difference in body length but a small difference in body weight. This separation of the mechanisms controlling bone growth and body weight increase was discussed. Part of the increased size of ovariectomised rats was attributed to increased skin size (and altered composition) and decreased tail length, giving decreased heat loss, and improved energy utilisation for growth. Body growth occurs in two overlapping phases, of cell hypertrophy and cell hyperplasia, represented by different growth equations, and controlled by different mechanisms. A possible mechanism controlling cell hypertrophy, and directing compensatory growth, based on cartilage growth, would explain some of the effects described. The endocrinology of the mechanism, and oestrogen's interaction with it, were discussed.