MATERIAL Y MÉTODOS

Experiment 2. 1

Statistical analysis was carried out using the Statistical Analysis System (SAS version 9. 1 , SAS Institute Inc., Cary, NC, USA, 2003). Live weight from D- l O until D268 was analysed using a linear model in the MIXED procedure with Period 1 , Period 2, Period 1 by Period 2 interaction, sex of calf, day of measurement and Period 1 by Period 2 by day of measurement interaction fitted as fixed effects. The random effects of farm of

origin, service sire and the random effect of heifer to allow for repeated measures were considered. Similarly, average daily liveweight gains from 0-2 to D268 were analysed using linear models in the MIXED procedure with Period 1 , Period 2 and Period 1 by Period 2 interaction fitted as fixed effects. Farm of origin and service sire were fitted as random effects. Average daily liveweight gain from D- l O to D-2 excluded the effect of Period 2 from the model, because this parameter was measured before Period 2 had occurred. Pre-calving and post-calving live weight were also analysed using a linear model in the MIXED procedure with Period 1 , Period 2 and Period 1 by Period 2 interaction fitted as fixed effects. The number of days pre-calving ( 1 -5) that a heifer was weighed was included as a covariable for pre-calving live weight only. Farm of origin of heifer and service sire were considered as random effects. Live weights from calving to weaning were analysed using a linear model in the MIXED procedure with Period 1 , Period 2 and Period 1 by Period 2 interaction, assistance at calving (0 = non­ assisted; l =assisted), day of measurement and the interaction of day of measurement with Period 1 and Period 2 as fixed effects and farm of origin of heifer, service sire, and heifer as random effects to allow for repeated measures. Body condition score pre­ calving was analysed using the GENMOD procedure with Period 1 , Period 2 and Period

1 by Period 2 interaction as fixed effects.

Plasma progesterone concentration was analysed as a repeated measure with the fixed effects of Period 1 , Period 2, Period 1 by Period 2 interaction, day of measurement and day of measurement with Period 1 and Period 2 interactions, and the random effects of farm of origin of the heifer, service sire and heifer to allow for repeated measures. Placental parameters were analysed using linear models in the MIXED procedure with treatments and treatment interactions considered as fixed effects and farm of origin of heifer and service sire as random effects. Sex of calf was considered as a fixed effect but was not significant so was excluded from the model. Models for placental parameters were run with and without birth weight of the calf as a covariable. Pearson correlation coefficients were calculated using the CORR procedure.

Birth weight of the calf and liveweight loss at parturition were analysed using a linear model in the M IXED procedure, with Period 1 , Period 2 and Period 1 by Period 2 interaction and sex of calf as fixed effects and service sire and farm of origin of heifer as random effects. Models were run with and without post-partum live weight of the heifer as a covariable. The model for liveweight loss at parturition also included the

Liveweight gain and birth weight - Experiment 2

number of days pre-calving that pre-calving live weight was recorded as a covariable. Linear models within the MIXED procedure were used for body dimensions, with birth weight of the calf as a covariable and sex of calf, Period 1 , Period 2 and Period 1 by Period 2 interaction as fixed effects. Service sire and farm of origin of heifer were fitted as random effects. Few (two) empty heifers at pregnancy diagnosis to detect second pregnancies meant no statistical analysis was carried out on this data.

Milk intake of calves was analysed using a linear model for repeated measures within the MIXED procedure. Fixed effects were sex of calf, Period 1 , Period 2, day of measurement, and Period 1 by Period 2 by day of measurement interaction. Date of birth of calf was fitted as a co variable and service sire, farm of origin of heifer, and calf were fitted as random effects. Similarly, live weights of calves from birth to weaning were considered as repeated measures using a similar model as for milk intake, except for the addition of grazing herd (early or late-calving). Grazing herd was considered as a random effect on milk intake but did not contribute to variation in the trait and was excluded from the model. Average daily liveweight gain of calves from birth to weaning was analysed using the same model as birth weight of the calf, however, sex of calf did not contribute to variation in this trait and was consequently excluded from the model.

Experiment 2.2

Live weights of heifers were analysed using a linear model for repeated measures with Period 1 , Period 2, day of measurement and interactions as fixed effects and farm of origin of the heifers and heifer as random effects. Live weights of calves were also analysed using repeated measures, with Period 1 , Period 2, day of measurement and interactions as fixed effects and calf as a random effect to allow for repeated measures. Days to calving and inter-calving interval were analysed using a linear model in the MIXED procedure, with Period 1 , Period 2 and Period 1 by Period 2 interaction as fixed effects. Pregnancy rate at pregnancy diagnosis to detect third pregnancies was analysed as a binomial trait using a logistic regression model in the GENMOD procedure after logit transformation. Period 1 , Period 2 and Period 1 by Period 2 interaction were fitted as fixed effects.

Resu lts

Experiment 2.1

Heifers

There were no differences among treatments in initial l ive weight (D-2 1 ) of the heifers. During the first treatment period, l iveweight gain of the heifers was 1 220 ± 1 20 g/day for the high treatment and 560 ± 1 10 g/day for the moderate treatment (P<O.OO l ). In the second period, heifers in the moderate treatment gained 540 ± 30 g/day, whilst heifers in the liveweight loss treatment lost 1 1 0 ± 30 g/day (P<O.OO l ). Mean daily liveweight gain from D93 to D268 was greater (P<0.05) for the HM and MM treatments compared with the HL and M L treatments (Table 6.2). Conversely, from day of parturition until L208, heifers in the HL and ML treatments grew faster than heifers in the HM and MM treatments.

These differences in rate of liveweight gain contributed to differences in live weights. At the end of the second treatment period (D93), the HM and MM groups were similar to each other, and were heavier than the HL and ML groups (P<0.05). Pre- and post­ partum live weight was greater for the HM and MM groups than for the HL and ML groups (P<0.05), but body condition score on D268 was greater for the HM and MM groups only compared with the M L group (P<0.05). On L208, the HM and HL groups no longer differed in live weight. Assisted heifers were lighter (P<0.05) than non­ assisted heifers throughout lactation.

Table 6.1 . LSM ± s.e. for liveweight gain (g/day) of heifers fed for high (H)