S. S. 2004. Association of a single nucleotide polymorphism in the bovine leptin gene with feed intake, feed efficiency, growth, feeding behaviour, carcass quality and body composition. Can. J. Anim. Sci. 84: 211-219. Leptin is a 16-kDa-hormone product of the obese gene synthesized and expressed predominantly by adipose tissues, which has been shown to play major roles in the regulation of body weight, feed intake, energy balance, fertility, and immune system functions. We report an investigation into the association of a previously identified cytosine to thymine missense mutation in exon 2 of the bovine leptin gene with feed intake, feed efficiency, growth, feeding behaviour, carcass quality and body composition in five genetic selection lines of a commercial population of beef cattle. Differences among genotypes in growth, feed intake and feed efficiency were not significant (P > 0.10) though steers homozygous for the thymine allele had positive residual feed intake (i.e., consumed more feed than expected) (+ 0.19 kg d -1 ) whilst steers homozygous for the cytosine allele had negative residual feed intake (-0.18 kg d -1 ). Steers carrying the thymine allele had a higher rate of gain in ultrasound backfat (P = 0.02), ultrasound backfat thickness (P = 0.06), higher carcass grade fat (backfat) (P = 0.005), lower yield grade (P = 0.01) and lower lean meat yield (P = 0.007). The thymine allele also tended to be associated with higher loin subcutaneous fat (P = 0.07) and was associated with higher brisket subcutaneous fat (P = 0.01), and brisket body cavity fat (P = 0.0001). No associations were found among the different genotypes and real-time ultrasound marbling, ultrasound longissimus thoracis area, carcass marbling and carcass longissimus thoracis area (P > 0.10). Our results show that animals carrying the thymine allele versus the cytosine allele may produce carcasses with poorer grades and lower lean meat yields but do not differ in carcass marbling or other fat depots.Key words: Beef cattle, leptin, feed intake, carcass merit Nkrumah, J. D., Li, C., Basarab, J. B., Guercio, S., Meng, Y., Murdoch, B., Hansen, C. et Moore, S. S. 2004. Association du polymorphisme d'un nucléotide du gène de la leptine bovine à la prise alimentaire, à la valorisation des aliments, à la croissance, aux habitudes alimentaires, à la qualité de la carcasse et à la composition corporelle. Can. J. Anim. Sci. 84: 211-219. La leptine est un dérivé hormonal 16-kDa du gène de l'obésité synthétisé et principalement exprimé par les tissus adipeux. On sait qu'elle joue un rôle important dans la régulation du poids, la prise d'aliments, le bilan énergétique, la fécondité et les fonctions du système immun. Les auteurs ont étudié l'association d'une mutation faux-sens entre la cytosine et la thymine rapportée antérieurement dans la partie exon 2 du gène de la leptine bovine avec la prise alimentaire, la valorisation des aliments, la croissance, les habitudes alimentaires, la qualité de la carcasse et la composition corporelle de cinq lignées d'...
. 2003. Evaluation of the National Research Council (NRC) nutrient requirements for beef cattle: Predicting feedlot performance. Can. J. Anim. Sci. 83: 787-792. The accuracy of predicted CowBytes ® versus actual dry matter intake (DMI) and average daily gain (ADG) of 407 Hereford × Angus and Charolais × Maine Anjou (445.6 ± 36 kg) feeder cattle using digestable enery acid detergent fiber (DE) estimated from the (ADF) content [Laboratory analysis method (LAB)] and from values determined in vivo (INVIVO method) was examined. The diet consisted of a 73.3% concentrate diet, 22.0% barley silage, 1.6% molasses, and 3.1% feedlot supplement fed ad libitum (as-fed basis). The calculated DE values of the feed were used to predict the metabolizable energy (ME), net energy of maintenance (NE m ), and net energy of gain (NE g ) of the diet. These energy values were then used in CowBytes ® to predict dry matter intake (DMI), ADG, and days on feed (DOF) necessary to meet targeted quality grade of AA and weights of 522 and 568 kg for the heifers and steers, respectively. There was no effect of gender and prediction method interaction (P > 0.10) on any of the variables measured. There were no (P > 0.05) differences in predicted DMI by either the INVIVO or LAB method but both methods underestimated DMI actually consumed by the cattle by 6.8 and 4.9% (P = 0.007), respectively. Indeed, regression values from these predictive methods and actual DMI were (P < 0.05) different from the one-to-one relationship expected by definition. In spite of the higher actual DMI, the actual ADG of the cattle was 14 and 11% (P = 0.0004) lower than was predicted by either the INVIVO or LAB methods. A possible reason for the lower ADG could be an overestimation of DE of the diet. Thus, if available, users of CowBytes ® should use actual DMI from their experience in ration formulation. In addition, the effects of environmental temperature on digestibility of diets should be taken into consideration when using the DE of the diet as determined from in vivo digestibility trials or calculated from chemical analyses in determining the DMI of feedlot cattle. . Les chercheurs ont utilisé la quantité d'énergie digestible de l'aliment pour prévoir les valeurs ME, NE m et NE g de la ration. Ensuite, ils se sont servis de ces valeurs avec le programme CowBytes ® pour prévoir l'IMS, le GQM et la durée de l'engraissement nécessaire pour obtenir une viande de qualité AA et un poids de 522 kg (génisses) ou 568 kg (bouvillons). L'interaction entre le sexe et la méthode de prévision n'a aucune incidence (P > 0,10) sur les variables examinées. Il n'y a pas d'écart (P > 0,05) entre l'IMS prévue par la méthode INVIVO et la méthode LAB, mais les deux sous-estiment l'IMS réelle des bovins de 6,8 % et de 4,9 % (P = 0,007), respectivement. De fait, les valeurs de régression des deux méthodes et l'IMS réelle ne rendent pas (P <0,05) la relation d'équivalence que laissait prévoir la définition des méthodes. Malgré une IMS plus élevée, le GQM réel des bovins était de 14 % et de ...
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