No abstract

. 1999. Estimates of direct and maternal genetic parameters for weight traits and backfat thickness in a multibreed population of beef cattle. Can. J. Anim. Sci. 79: 433-439. Variance components were estimated for weight at birth, weaning, and 365 d of age, and yearling ultrasonic backfat thickness in a multibreed population of beef cattle. Data (n = 5880) were available on F 1 animals and various crosses leading up to, and including, a composite breed (7/16 British, 1/4 Charolais, 1/4 Simmental, and 1/16 Limousin). Single-and two-trait analyses were conducted using an animal model and derivative-free REML procedures. Covariates representing fractional contributions of each of the four purebred groups and average heterotic effects, both direct and maternal, accounted for breed composition. Direct and maternal genetic, maternal permanent environmental, and residual effects were the random variables. Only minor differences existed between parameter estimates obtained from the various analyses. Mean direct heritabilities were 0.51, 0.33, 0.48, and 0.37 for weight at birth, weaning, and 365-d, and backfat, respectively, which, though well within the range of published estimates, seemed higher than average, indicating diversity in the founding purebreds. Mean maternal heritabilites were 0.09, 0.13, and 0.08 for the three consecutive weights. A likelihood ratio test showed maternal heritability and(or) the direct-maternal correlation was important (P < 0.001) for 365-d weight. Averaged across weights, the direct-maternal correlation was 0.07, lacking evidence of genetic antagonism. No age of dam or random maternal effects on backfat were apparent. Phenotypic correlations between weight at birth and weaning and weight at weaning and 365-d were 0.46 and 0.76, respectively. Though moderate between birth and weaning weight, maternal genetic and permanent environmental correlations between weaning and 365-d weight approached unity, demonstrating maternal carryover effects. Phenotypic and genetic correlations of 0.19 and -0.13, respectively, implied a limited association between 365-d weight and backfat, which possibly would have been stronger had fat been measured later in life. Estimates of variance components suitable for general use can be obtained from data from multibreed animals by considering breed and heterotic effects. Des covariants représentant les contributions proportionnelles de chacun des quatre groupes de race et les effets hétérotiques moyens, tant directs que maternels, prenaient en compte la composition génétique des animaux. Les effets génétiques directs et maternels, les effets environnementaux permanents maternels et les effets résiduels constituaient les variables aléatoires. Seules des différences minimes apparaissaient entre les valeurs paramétrales obtenues des diverses analyses. Les coefficients d'héritabilité directe moyens étaient, respectivement, de 0,51, 0,33, 0,48 et 0,37 pour le poids à la naissance, au sevrage et à 365 jours et pour l'épaisseur du gras de couverture. Ces chiffres, bien que...

. 2004. Time of feeding and growth promotant effects on the winter growth performance and carcass traits of steers. Can. J. Anim. Sci. 84: 133-144. The effects of time of day of feeding and estrogenic growth promotant on growth performance and carcass traits were determined in three experiments conducted over 3 yr (winters 1998-1999, 1999-2000, 2000-2001). Crossbred steers (year 1, n = 144, year 2, n = 128, year 3, n = 144) were assigned at fall weaning on the basis of sire, age (190 ± 21 d, mean ± SD), and body weight (244 ± 34 kg) to one of eight pens in an outdoor lot at the Brandon Research Centre (49°54″N). In years 1 and 2, pens were assigned to either morning-fed (MF, 0900) or evening-fed (EF, 2000) treatments, and steers within pen were assigned to either Synovex Plus ® (TAE) or Synovex S ® (PE) growth promotants. In year 3, pens were assigned to either TAE or PE treatments and all were evening-fed. Beginning on Nov. 09 (0 d), steers were given a 20% hay, 80% concentrate (79.2% barley, 0.8% premix) mixed ration (88.6% dry matter, 13.7 MJ kg -1 digestible energy, 124 g kg -1 crude protein, 33.6 mg kg -1 lasalocid). Diets were fed, once daily, in amounts that were consumed before the next feeding, until steers were marketed. Growth promotants were administered at 0 and 84 d. The winter of year 2 was warmer (P < 0.05) than, and years 1 and 3 similar (P > 0.05) to, the 30-yr average ambient temperature (-8.8°C and -12.9°C, respectively). Evening feeding increased (P < 0.05) gain in body weight, especially in year 2 and backfat, especially in year 1, and this was reflected in heavier (P < 0.05) carcass weight in year 2, and whiter (P < 0.05) fat and greater (P < 0.05) rib eye moisture in year 1 and overall reduced (P < 0.05) feed cost of gain in winter. In all 3 yr TAE, relative to PE, produced greater (P < 0.05) body weight gain, and heavier, leaner carcasses with greater (P < 0.05) rib eye area, coarser (P < 0.05) meat texture and greater (P < 0.05) shear force, and reduced (P < 0.05) the feed cost of gain. Time of feeding and choice of growth promotant have significant potential to reduce the business risk of feeding steers in winter. Les auteurs ont étudié les effets du moment du repas et des oestrogènes employés comme accélérateur de croissance sur le rendement des bouvillons et les caractéristiques de la carcasse dans le cadre de trois expériences effectuées chacune une année distincte (hivers de 1998-1999, de 1999-2000 et de 2000-2001). Au moment du sevrage automnal, ils ont réparti des bouvillons hybrides (1 re année, n = 144; 2 e année, n = 128; 3 e année, n = 144) dans 8 enclos extérieurs en fonction du géniteur, de l'âge (190 ± 21 j, moyenne ± É.-T.) et du poids (244 ± 34 kg), au centre de recherche de Brandon (49°54″N). Les deux premières années, les animaux de chaque enclos ont été nourris le matin (9 h) ou le soir (20 h) et chaque animal de l'enclos a reçu l'accélérateur Synovex Plus ® (TAE) ou Synovex S ® (PE). La troisième année, les animaux ont tous été nourris en soirée et ont reçu un des...

R. 2001. The effects of gonadotrophin releasing hormone in prostaglandin F 2α α -based timed insemination programs for beef cattle. Can. J. Anim. Sci. 81: 335-343. Trials were conducted in the spring (May; n = 324) and fall (October; n = 132) with crossbred continental-type beef cows assigned on the basis of parity and postpartum interval to one of three timed-AI treatments and one of two post-AI treatments. The timed-AI treatments were: (DPG) double (14 d apart) PGF 2α (Lutalyse ® ) and AI (day = 0) 72 h after the second PGF 2α (day -3); (OVS) Ovsynch ® with the second GnRH (Factrel ® ) at 48 h and AI at 66 h; and (BRC) the same as OVS except that the second GnRH was given at the time of AI. Half of the cows within each treatment were given GnRH on day 14. Plasma progesterone concentrations were determined for the day of the first injection and on days -3, 0, 14, and 21. Timed-AI pregnancy was diagnosed by ultrasonography at day 42 and confirmed at calving. For DPG, OVS and BRC, PGF 2α responder rates were 75.9, 51.4 and 71.3%, respectively, in spring (P < 0.05) and 70.4, 70.4 and 59.1% in fall (P > 0.05), and AI pregnancy rates were 28.7, 44.9 and 44.4% in spring (P < 0.05) and 25.0, 40.9 and 43.2% in fall (P > 0.05). Post-AI GnRH had no significant effect on pregnancy or conception rates or day 21 progesterone. The use of GnRH in the PGF 2α based timed-AI program improved pregnancy rates and the BRC treatment was as effective as OVS. Neither postpartum interval nor initial progesterone concentration influenced (P > 0.05) the effect of GnRH on AI pregnancy rate, and GnRH had no effect (P > 0.05) on twinning rate or gender ratio.

Crossbred beef heifers (n = 144) were assigned at weaning (187 ± 14 d of age) by body weight (225 ± 23 kg) and sire breed (British/Continental) to one of two photoperiod treatments from 21 Decem ber 1998 (0 wk) until 10 May 1999 (20 wk): natural photoperiod (NP) that gradually increased from 8.1 h (0 wk) to 15.2 h (20 wk) and, extended photoperiod (EP) that consisted of natural + supplemental light (400 lx, 1 m above ground) to extend photoperiod to 16 h. Rations were formulated for two-steps of body weight gain (0.6 and 1.2 kg d-1) to achieve 60% of mature weight at 18 wk. Visual observations of estrus behavior were made twice daily and confirmed by serum progesterone. Body weight, backfat and serum prolactin data were determined for each 4-wk period. Ambient temperatures averaged -12.2 ± 6°C in winter (0 to 12 wk) and 4.2 ± 5°C in spring (12 to 20 wk). Gain in body weight was greater (P < 0.05) and backfat lower (P < 0.05) for EP than NP treatments from -2 to 6 wk and only 1% of heifers had attained puberty during this period. However, as yearlings at similar (P > 0.05) body weight and backfat, more (P < 0.05) EP than NP heifers had attained puberty (84.7% vs. 69.4%). Prolactin was greater (P < 0.05) for EP than NP treatments from 2 to 6 wk (10.3 vs 5.5 ± 1.2 ng mL-1). Management of photoperiod influences attainment of puberty and prolactin secretion in beef heifers housed in an outdoor environment. Key words: Photoperiod, puberty, estrus, beef heifers, prolactin