Browsing by Author "Roca Fraga, Fernando Javier"

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Optimum nutrition of the pregnant ewe : a meta-analytic approach : a thesis presented in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Animal Science at Massey University, Manawatū, New Zealand
(Massey University, 2017) Roca Fraga, Fernando Javier
Formal systematic review guidelines and meta-analytic methods were used in the present study to achieve three main objectives. Firstly, literature on the effect of ewe nutrition during pregnancy on fetal and postnatal lamb growth was reviewed and effect sizes estimated for fetuses/lambs at three stages of their life: 1) late gestation fetal weight (LGFW), 2) lamb birth weight (BW) and 3) weaning weight (WW). Secondly, the contribution of experimental factors responsible for variation in study results was determined. Thirdly, a field trial was conducted to increase understanding in an area identified by the meta-analyses as requiring further experimentation. Overall, early- and mid-pregnancy undernutrition had no significant effect on LGFW (β[Early-pregnancy] = -0.0007, 95% Highest posterior density (HPD) = -0.26 to 0.28; β[Mid-pregnancy] = -0.07, 95% HPD = -0.27 to 0.16), BW (β[Early-pregnancy] = 0.01, 95% HPD = -0.36 to 0.34; β[Mid-pregnancy] = -0.02, 95% HPD = -0.36 to 0.33) and WW (β[first 100 days of pregnancy] = -0.008, 95% HPD = -0.42 to 0.18), suggesting that short to moderate periods of undernutrition in these stages are tolerated by ewes with limited impact on their offspring, when nutrition is re-established to pregnancy maintenance (PM) or above levels during late-pregnancy. Late-pregnancy undernutrition can significantly decrease LGFW and BW by up to 1.15 kg at birth, with residual effects at weaning resulting in weaned lambs that are up to 18% lighter than their control counterparts and thus, should be avoided. The present study also considered the effect of maternal above PM feeding on LGFW, BW and WW. The combined effects across these studies were variable, as few experiments investigated above PM feeding at each stage of pregnancy, and thus it was not possible to draw definitive conclusions. A field experiment was undertaken to determine the effects of ad-libitum (AL) feeding at various stages of pregnancy and for differing lengths of time on twin lamb BW and WW. Results showed that providing ewes with AL feeding significantly (p<0.05) increased their live weight and BCS, but did not increase (p>0.05) the BW or WW of their lambs relative to their control counterparts. This study also suggested that AL feeding during late-pregnancy may have negative consequences to the survival of twin lambs and requires further examination. Thus, AL feeding is not justified as a management tool to increase twin lamb BW and WW, when nutrition is adequate during lactation. The present study represents the first meta-analytic approach examining the effect of changes in the ewe nutrition during pregnancy on the growth of offspring at various developmental stages. Given the complex interrelationship between nutrition of the pregnant ewe, her reproductive success, fetal growth and development, and offspring post-natal performance, no single study can provide a definitive understanding of responses to a particular treatment and there is value in combining available experimental evidence to elucidate a more global picture. A meta-analytic approach can find trends in combined data that would otherwise be overlooked using traditional review methods and can also identify gaps in current knowledge.
Prediction of milk yield of 3-year-old Angus cows and the influence of maternal milk production on the postnatal growth of beef steers : a thesis presented in fulfilment of the requirements for the degree, Master of Sicnece (Animal Science), Massey University, Palmerston North, New Zealand
(Massey University, 2013) Roca Fraga, Fernando Javier
Maternal milk production influences calf weaning weight which is the major driver for economic return in a cow-calf operation. The objective of this study was to use measures of calf milk intake to estimate milk production of Angus (AA; n=43), Angus×Friesian (AF; n=32), Angus×Jersey (AJ; n=40) and Angus×Kiwi-Cross (AK; n=21) cows, and to determine how milk yield was related to calf growth rate (n=64) from birth to one year of age. Milk production was estimated by the weigh-suckle-weigh (WSW) technique at an average 32, 49, 80, 120 and 160 days (D) post-partum. Third-order Legendre polynomials were fitted to milk data using random regression to estimate the lactation curve for each cow. Live weight of all steers was recorded at birth and thereafter accompanying every WSW measurement. Postweaning live weight was recorded at an average D240, D330 and D350 of age. Growth curves for each steer were estimated by fitting third-order Legendre polynomials to live weight data using random regression. The average total milk production from D32 to D160 was 1337 ± 22 kg for AF cows, 1245 ± 20 kg for AJ cows, 1301 ± 32 kg for AK cows and 1017 ± 20 kg for Angus cows. The AF, AJ and AK cows produced more (P<0.05) milk from D32 to D160 than the AA cows. The AF cows produced more (P<0.05) milk than AJ cows, with AK cows being intermediate and not differing (P>0.05) from either AF or AJ cows. Crossbred cows produced more milk (P<0.05) at all stages of lactation when compared with straightbred AA cows. In the present study, as the proportion of Friesian or Jersey in the crossbreds increased from 0 to 50%, an extra 325 kg and 240 kg of milk, respectively, was expected compared to the AA cows. Total energy intake from milk was higher (P<0.05) for the AF-, AJ- and AK-reared steers compared to those reared by AA dams. This resulted in higher liveweight gains so that steers reared by crossbred cows were heavier (P<0.05) from D60 to D270 than those reared by AA cows. Results also revealed that the higher live weight at D60 in AJ-reared steers compared to AA-reared steers was due to differences in milk consumption from D32 to D60. The higher live weight of AF- and AK-reared steers at D60 compared to AA-reared steers was attributed to a maternal effect on steer size; however, from D90 until weaning at D160, any differences in live weight were due to differences in milk consumption. Estimation of the theoretical pasture consumption revealed that AA- reared steers compensated for the lower milk intake by eating more grass, however, this was not enough to support high daily gains during the pre-weaning period. The differences in live weight seen at weaning between steers were maintained post-weaning until D270 and were attributed to differences in milk consumption during the pre-weaning period. Under nonlimiting nutrient availability, AF, AJ and AK cows were able to pr