RESUMO
Muddy pens can negatively affect welfare and performance of feedlot beef cattle. In some regions with temperate weather, plastic greenhouse covers, above the entire pens are used to fatten cattle in a clean and dry environment. The objective of this research was to investigate effects of greenhouse roofed pens on beef cattle feedlot performance in temperate weather. Data were collected from a feedlot located in Central Mexico between 2016 and 2019. The study included 1,062 closeouts of pens with 68,305 crossbred bulls fed in pens with or without a greenhouse roof. Feeding ranged from 82 to 210 d, depending on the initial weight of cattle, which ranged from 255 to 511 kg. For each pen, average daily dry matter intake (DMI; kg of DMI·animal-1·d-1), average daily gain (ADG, kg·animal-1·d-1), and feed efficiency (G:F, ADG/DMI) were measured. Factorial analyses were performed to test the interaction and main effects of initial weight grouping (light, medium, and heavy), roof, and season as fixed effects, and year as a random effect. None of the three-way interactions were significant (P > 0.51). There was no initial weight grouping × roof interactions for DMI and ADG (P > 0.31). There was (P = 0.03) an initial weight grouping × roof interaction for G:F, as pens of all initial weight groups had greater (P < 0.01) G:F in pens with greenhouse roof than its counterpart in pens without greenhouse roof, but the advantage was greater for pens with light cattle (0.178 vs. 0.166; P < 0.01). There was no initial weight grouping × season interactions for all variables (P > 0.39). There was no roof × season interaction for DMI (P = 0.47), but there were interactions for ADG and G:F (P < 0.01). The ADG was not different (P > 0.13) during summer and autumn based on the roofing system, but pens with greenhouse roofs had greater ADG during spring (1.70 vs. 1.61) and winter (1.68 vs. 1.64; P ≤ 0.01). The G:F was greater (P < 0.01) in all seasons for pens with a greenhouse roof, with the most prominent advantage during spring (0.173 vs. 0.160). There were main effects for cattle initial weight grouping and roof for all variables (P < 0.01). Season affected DMI and G:F (P < 0.01). Pens with greenhouse roofs had decreased DMI (9.70 vs. 9.86), greater ADG (1.67 vs. 1.63), and increased G:F (0.173 vs. 0.166) compared to pens without greenhouse roofs (P < 0.01). Pens with greenhouse roofs in feedlots located in temperate regions positively affect beef cattle performance.
RESUMO
The ultimate goal of genetic selection is to improve genetic progress by increasing favorable alleles in the population. However, with selection, homozygosity, and potentially harmful recessive alleles can accumulate, deteriorating genetic variability and hampering continued genetic progress. Such potential adverse side effects of selection are of particular interest in populations with a small effective population size like the Romosinuano beef cattle in Mexico. The objective of this study was to evaluate the genetic background and inbreeding depression in Mexican Romosinuano cattle using pedigree and genomic information. Inbreeding was estimated using pedigree (FPED) and genomic information based on the genomic relationship matrix (FGRM) and runs of homozygosity (FROH) of different length classes. Linkage disequilibrium (LD) was evaluated using the correlation between pairs of loci, and the effective population size (Ne) was calculated based on LD and pedigree information. The pedigree file consisted of 4875 animals born between 1950 and 2019, of which 71 had genotypes. LD decreased with the increase in distance between markers, and Ne estimated using genomic information decreased from 610 to 72 animals (from 109 to 1 generation ago), the Ne estimated using pedigree information was 86.44. The reduction in effective population size implies the existence of genetic bottlenecks and the decline of genetic diversity due to the intensive use of few individuals as parents of the next generations. The number of runs of homozygosity per animal ranged between 18 and 102 segments with an average of 55. The shortest and longest segments were 1.0 and 36.0 Mb long, respectively, reflecting ancient and recent inbreeding. The average inbreeding was 2.98 ± 2.81, 2.98 ± 4.01, and 7.28 ± 3.68% for FPED, FGRM, and FROH, respectively. The correlation between FPED and FGRM was -0.25, and the correlations among FPED and FROH of different length classes were low (from 0.16 to 0.31). The correlations between FGRM and FROH of different length classes were moderate (from 0.44 to 0.58), indicating better agreement. A 1% increase in population inbreeding decreased birth weight by 0.103 kg and weaning weight by 0.685 kg. A strategy such as optimum genetic contributions to maximize selection response and manage the long-term genetic variability and inbreeding could lead to more sustainable breeding programs for the Mexican Romosinuano beef cattle breed.
