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Objective: To evaluate the J-Synch protocol with two eCG doses in beef heifers during the summer in northeastern Mexico. Design/Methodology/Approach: 218 heifers (109/treatment) with a body weight of 350±12.1 kg were used. A J-Synch protocol was applied in order to evaluate two eCG doses: T1 (250 IU) and T2 (300 IU). Subsequently, the total number of heifers from both treatments were inseminated at a fixed time (FTAI): 72 h after removing the device. Results: No significant differences (p>0.05) were recorded in the estrous percentage at first service (T1=91%; T2=96%) and in the repeating heifers (T1=25.2%; T2=19.2%). The insemination technician and coat color variables impacted the estrous percentage in repeating heifers. The pregnancy percentage at first service was 64.8% and 70.1% for T1 and T2 (p>0.05), respectively. The insemination technician had a variable effect on the pregnancy percentage, from 63.4% (the best-qualified technician) to 48.6% (the technician who obtained the lowest percentage). Study Limitations/Implications: The pregnancy rate in beef heifers will depend mainly on the experience and skill of the insemination technician. Findings/Conclusions: The same results were obtained regarding the presence of estrous and pregnancy in beef heifers during the summer season, either with 250 or 300 IU of eCG. [ABSTRACT FROM AUTHOR]

Objective: To quantify the percentage of breeding heifers slaughtered and the stage of gestation of the product in the municipal slaughterhouse of Pijijiapan, Chiapas. Approximation: Many breeding heifers are sent to the slaughterhouse due to various factors, such as the few gestations diagnostic tests carried out in the field and erroneous diagnoses. Another cause is the dry season, in which the forage capacity is reduced, and the producer must dispose of animals in his productive unit, including breeding heifers, thus decreasing the cattle herd population. This situation can be considered an animal welfare problem. Methodology: The total number of cattle slaughtered in four months was recorded, as well as the number of females, and it was recorded whether they were pregnant or not, and the gestation period of the calf. Results: Cattle individuals (428) were slaughtered, of which 399 were females (93.22%) and 29 males (6.78%). Of the females, 211 (53%) were pregnant, 39.81% in the first third of gestation, 27.48% in the second and 32.22% in the third. Limitations: It is necessary to increase the study period and not only in this municipality but also to implement similar research in other slaughterhouses in Chiapas to understand this problem better. [ABSTRACT FROM AUTHOR]

Objective: To assess antibiotic use and other factors associated with death rates in beef feedlots in 3 regions of the US over a 10-year period. Sample: Data for 186,297 lots (groups) of finished cattle marketed between 2010 and 2019 were obtained from a database representing feedlots in the central, high, and north plains of the US. Procedures: Descriptive statistics were generated. Generalized linear mixed models were used to estimate lot death rates for each region, sex (steer or heifer), and cattle origin (Mexico or the US) combination. Death rate was calculated as the (number of deaths/number of cattle placed in the lot) × 100. Lot antibiotic use (TotalActiveMG/KGOut) was calculated as the total milligrams of active antibiotics assigned to the lot per live weight (in kilograms) of cattle marketed from the lot. Rate ratios were calculated to evaluate the respective associations between lot death rate and characteristics of cattle and antibiotic use. Results: Mean death rate increased during the 10-year period, peaking in 2018. Mean number of days on feed also increased over time. Mean TotalActiveMG/KGOut was greatest in 2014 and 2015, lowest in 2017, and moderated in 2018 and 2019. Death rate was positively associated with the number of days on feed and had a nonlinear association with TotalActiveMG/KGOut. Feeding medicated feed articles mitigated death rate. Conclusions and clinical relevance: Results suggested a balance between disease prevention and control in feedlots for cattle with various risk profiles. Additional data sources are needed to assess TotalActiveMG/KGOut across the cattle lifetime. [ABSTRACT FROM AUTHOR]

The National Institute of Forestry, Agricultural and Livestock Research (INIFAP) in Mexico has been studying the Criollo Coreño (C) cattle of the Sierra Madre Occidental for over 20 yr. This review covers productive, genetic and molecular characterization, as well as short-, medium- long-term research challenges and outlooks. Evaluations have been done of 35 growth, carcass quality, fertility and milk production traits in C, Guzerat (G), CG and GC cattle generated through diallelic crossing. Individual heterosis was found to affect reproduction and milk production, while maternal heterosis influenced kilograms of calf weaned per cow exposed. Direct and maternal genetic effects had no relevant influence on the analyzed variables. In other studies, C bulls fed high energy diets were found to produce meat with favorable fatty acid profiles and good quality carcasses, while low doses of FSH can be used for superovulation in C heifers, without affecting embryo production. Overall, the results indicate that GC cows are the best option for calf production, and that the C population maintains significant levels of genetic diversity. Further genetic diversity research is needed on Mexican Criollo cattle populations using molecular genetics; Criollo herds must be included in the systematic recording of phenotypes of productivity and adaptability to be able to identify genes of interest unique to Criollo cattle. [ABSTRACT FROM AUTHOR]

The National Institute of Forestry, Agricultural and Livestock Research in Mexico has been active for decades in researching genetic improvement in beef cattle. This review uses master theses, congress papers and scientific articles published from 1987 to 2020 to summarize much of the relevant research, and addresses research challenges and outlook over the short-, medium- and long-term in this area. Research done over the last 34 yr has evaluated the productive and reproductive performance of Bos indicus and Bos taurus x Bos indicus beef cattle raised under tropical conditions. Multibreed genetic evaluations have been done for Simmental-Simbrah and Charolais-Charbray populations in Mexico. Analyses have quantified the importance of maternal effects on growth traits, and estimated heritability and genetic correlations for growth and reproductive traits in male and female Bos taurus and Bos indicus animals. The genotype-environment interaction has been confirmed to influence expression of weaning weight in Simmental cattle. Age adjustment factors have been developed for maternal age for weights at birth and weaning, and prototypes of national genetic evaluation were developed for stayability and heifer fertility. Genetic diversity has been quantified for Simmental, Charolais and Simbrah populations, and SNPs identified that are associated with growth traits in Simmental and Simbrah populations. Short-term goals include development of selection indices and prediction of the genetic merit of carcass traits. Over the medium-term, emphasis is needed on genomic evaluations for tolerance to heat stress, residual feed intake and health traits, while in the long-term the goal is to make interbreed genomic predictions. [ABSTRACT FROM AUTHOR]

The analysis of the value chain in beef cattle of Mexico has focused mainly on production and final consumer; however, slaughter centers represent the main link between producers and consumers. The objective was to analyze the demand for live beef cattle in the slaughter centers of Mexico, 2000-2018. The sample considered 50 slaughterhouses, in 26 of 32 states and the demand models were estimated using the ordinary least squares method. It was possible to estimate the four best demand models by product; the price explained 43.4 % of the variability in the quantity of beef in the slaughter centers; 60.4 % for cull cows, 37.7 % steers, 33.5 % cull bulls and 28.8 % heifers. All products behaved inelastic in price (-0.17), but the demand for steers had the lowest elasticity (-0.06). The beef market presented a low average density of connections between the producers and slaughter centers analyzed (25.2 ± 43.4 %), which indicates its inefficiency. The state of Jalisco represented the main slaughter center in steers and cull cows, while Aguascalientes in heifers and cull bulls. [ABSTRACT FROM AUTHOR]

Objective: To identify the factors that affect the onset of ovarian activity in prepuberal heifers in the Huasteca Veracruzana of Mexico. Design/Methodology/Approach: Samples were taken from animal production units of the municipality of Tantoyuca, Veracruz. The onset of ovarian activity was determined by the presence of ovarian follicles and corpus luteum by ultrasonography technique. Zoometric indices and body condition were calculated at the same time, and the zootechnical practices that were applied to the animals in the last six months before the sampling day were registered. A survey was applied to characterize the management of animal production units; the main topics in the survey were: health, reproduction, nutrition, and suckling. All animals available within selection criteria in the production units were sampled. A multiple linear regression (Statistical Analysis Software Version 9.4) and cluster analysis (R Studio Version 1.1.419) were used to identify the main categorical variables that affected the model. Results: The onset of ovarian activity depends mainly on the anatomical development of the heifers. The biostimulation (male effect) on the heifers has an important effect on reducing the age at puberty. Study Limitations/Implications: The study was developed during a long drought period in the region. Findings/Conclusions: The genetic mosaic of the evaluated animals in the production units did not affect the onset of ovarian activity of the heifers; however crossbred heifers (Bos taurus X Bos indicus) begin the ovarian activity younger. [ABSTRACT FROM AUTHOR]

Sixty crossbred heifers (371 ± 7 kg) were used in a 63-d feeding trial (4 pens per treatment in a randomized complete block design) to evaluate the influence of dietary supplementation with zilpaterol hydrochloride (β-agonist) or with different levels of chromium-enriched live yeast (Cr-YC) on growth performance and carcass characteristics. Heifers were fed a diet based on steam-flaked corn (1.45 Mcal of net energy of gain, NEg kg-1). Treatments were: 1) control, no yeast, no zilpaterol supplementation (Ctrl); treatments 2, 3 and 4) were the same basal diet supplemented with a commercial Cr-YC for a final dose of 10, 20 or 30 g hd-1 d-1 of yeast strain, and 5) the same basal diet (Ctrl) supplemented with 6 mg of zilpaterol kg-1 of feed for 30 d (ZIL), drug withdrawn from the diet 3 d pre-harvest. Compared with controls, ZIL increased final weight (3.8 %, P < 0.03), carcass-adjusted daily gain (18.7 %, P = 0.05), apparent dietary net energy of maintenance (14 %, P < 0.01), and decreased observed/expected DMI (14 %, P < 0.01). Treatment with ZIL did not affect (P < 0.13) marbling score, but, compared with control group, increased carcass dressing percentage (2.6 %, P = 0.01), and reduced (P = 0.02) kidney, pelvic and heart fat (KPH, 19.8 %) and fat thickness (9.4 %) and tended (5.9 %, P = 0.06) to increase Longissimus muscle area. Compared with Cr-YC treatments, ZIL increased apparent dietary NEm (P = 0.03) and dressing percentage (P < 0.01), and decreased observed/expected DMI (P = 0.03) and KPH (P=0.04). Treatment with Cr-YC did not affect carcass characteristics, but compared with control, Cr-YC supplementation tended to increase final BW (P = 0.08), ADG (0.09), fed:gain ratio (F:G, P = 0.08) and dietary NE (P = 0.06). Level of supplemental Cr-YC increased (linear component, P ≤ 0.04) final BW, ADG, F:G, apparent dietary NEm, and decreased (P = 0.02) observed/expected DMI. Level of supplemental Cr-YC did not affect (P ≥ 0.33) dressing percentage, LM area or marbling score, but, fat thickness and KPH decreased (P = 0.02) as Cr-YC level supplementation increase. DMI and HCW tended (P ≤ 0.08) to increase with increasing Cr-YC supplementation level. It is concluded that, zilpaterol supplementation increase growth performance in heifers as results of greater muscle accretion and for reduction of body fat. Chromium-enriched yeast supplementation increase growth performance and dietary NE, with modest effect in carcass characteristics. Better responses were observed at level of Cr-YC supplementation of 30 g hd-1 d-1 that corresponds to daily intakes of 1.65 x 1011 colony forming units and 15 mg chromium. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to characterize and compare bovine cattle slaughtered in Sonora relative to carcass physico-chemical, morphometric and yield characteristics. One hundred and sixty one (161) carcasses from steers and heifers of native cattle from two producers (A, B) were assessed, showing differences (P<0.05) for live, hot and cold weights, being higher for B, as well as yield (more than 60 %). Cattle from both producers showed carcasses with rib eye areas of 80.7 cm2 for A and 82.2 cm2 for B, and average fat thickness of 9.4 and 9.0 mm, respectively. Shear force for meat showed high values in cattle of both producers, (8.5 and 7.9 kgf), and therefore tenderness can be classified as intermediate. Color showed no differences (P 0.05), for value a*, corresponding to fresh meat shades, but significant differences for L* and b* were observed, although no DFD (dark, firm and dry) meat was detected. In cattle of both producers, temperature in the semimembranous muscle was higher 45 min and 24 h post mortem, while the final pH ranged between 5.61 and 5.72. Morphometric measurements and compaction index, showed differences between cattle from both producers (P>0.05). Boning yields (P>0.05) showed differences for carcass weight, but no relationship between carcass weight and tissue composition in each fraction was found. [ABSTRACT FROM AUTHOR]

The present work was carried out at the ranch "La Piramide" in the town of Aldama, Tamaulipas. The effect of three different supplementation levels was evaluated (3, 4 and 5 kg of concentrated cow-1 day-1) for milk production and body weight of first-calf heifers under grazing conditions. The cows were fed star grass (Cynodon nlemfuensis) and the supplement provided contained 18.0% of crude protein. 30 nursing Swiss Brown x Zebu heifers were used, with an average weight of 367.1 ± 29.6kg. A random design was used with three treatments and 10 repetitions (cows) for treatment. The average milk production was 7.7 ± 1.0kg day-1. The mean final body weight was 395.8 ± 21. 1 kg. In both cases there were no significant differences (P > 0.05) observed due to treatments. The results in this study conclude that supplementation of concentrate did not affect the milk production and the heifers body weight. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to assess the ovarian response and the percentage of gestation in Mexican tropic''s heifers treated with melengestrol acetate (MGA). The work took place in the municipality of Tzitzio, Michoacán, Mexico. Twenty-five, 43±4.6 months old heifers, weighting 312.72±25.78kg, and recording 3.0±0.25 of body condition were feded with 0.5mg of MGA pre-blended with 250g of supplement through 21 days. At the end of the treatment the heifers ovaries were observed over ultrasonography daily until the ovulation time, and then four more times every 5 days to observe the corpus luteum development. The heifers were direct mated, and 88% of them revealed dominant follicle post- treatment, and had their ovulation on the fifth to tenth day, focused on the eighth day (72.7%). Most of them (95.5%) were pregnant after the mating; realizing that ovaric response of the heifers treated with MGA at a dose of 0.5mg per day through 21 days standarize the estrous advent. Moreover, it shows that the ovum have the conditions to be fertilized. The MGA may be used as an important constituent to perform a strategy to achieve homogeneous calves lots in suitable times for production, thus contributing to the Mexican tropic''s livestock reproductive parameters improvement. [Copyright &y& Elsevier]

• Strong genetic correlations were found between scrotal circumference and stayability. • Strong genetic correlations were found between heifer fertility and stayability. • Stayability of Charolais–Charbray cattle can be improved through scrotal circumference. • Stayability of Charolais–Charbray cattle can be improved through heifer fertility. Records from Charolais, Charbray and Charolais-Zebu crosses provided by Charolais–Charbray Herd Book de México, were used to estimate heritabilities and genetic correlations between scrotal circumference (SC, n = 18,972), heifer fertility (HF, n = 91,250), and stayability (STAY, n = 17,696). Measurements of SC were adjusted to 365 days limiting the age range from 320 to 410 days of age. The trait HF was coded as 1 if the heifer calved before 1,281 d of age and 0 otherwise. The trait STAY was defined as the probability of whether or not a cow calved a second calf before the six years of age given that, at least, the cow had calved a calf at three years of age or before. A three trait animal model and a Bayesian linear-threshold-threshold analysis were used to estimate (co)variance components. Heritability estimates were 0.18 ± 0.02, 0.11 ± 0.01, and 0.26 ± 0.03 for SC, HF and STAY, respectively. Strong genetic correlations were detected between SC and STAY (0.76 ± 0.04), and between HF and STAY (0.57 ± 0.07), suggesting that selection of sires based on SC, and HF could lead to an improvement of STAY of cows in the Charolais–Charbray population of Mexico. A weak genetic correlation was found between SC and HF (−0.08 ± 0.10). Overall, the heritabilities and genetic correlations estimated for the three traits evaluated in this study support the feasibility of improving by selection the reproductive performance of the Charolais–Charbray population of Mexico. [ABSTRACT FROM AUTHOR]

The objective of this study was to compare the fertility of Holstein heifers under cooling and inseminated with sexed semen during the summer versus winter season. Eighty heifers were divided into two groups: (1) summer group (n = 40), consisted of heifers under visual heat detection and inseminated with sexed semen. These heifers were also provided with artificial cooling under shade area from 1000 to 1800 h. (2) Winter group (n = 40), heifers under shade only and with the same reproductive protocol than the summer group. The rectal temperature and respiratory rate were higher (P < 0.05) in the summer group. Vaginal temperature presented higher values in summer (P < 0.05) in most of the daylight hours except between 1100 and 1200 h (P > 0.05). Progesterone, as measured from the AI to 21 days after AI, showed higher values (P < 0.05) in days 6, 12, 18, and 21 during summer compared with winter in pregnant heifers; also, non-pregnant heifers had higher concentrations of progesterone on days 6, 9, 15, and 21 (P < 0.05) in winter. The conception rate in winter at day 35 post-AI (65%) was higher (P < 0.05) than those observed during summer (37.5%). In conclusion, although the lower fertility observed during summer with sexed semen, it can be considered as normal and comparable to the conception rate with conventional semen under hot climate.

The objective of the work was to evaluate the impact of the CHAPINGOAGROPEC Star Integral Advising and Consultancy Strategic Model in the development of a dairy farm in the state of Jalisco, Mexico from January, 2004 to December 2005. The model consisted in: 1. Advisor actualization. 2. Use of computer technology tools, AGROPEC Star software and Internet in the process; 3. Elaboration of an integral, cooperative diagnosis and strategic analysis. 4. Elaboration, implementation and following of a Strategic Plan of Re-engineering Processes (SPRP) for the identified problems. 5. Pursuit and integral evaluation of the farm and the adviser. 6. Training programs for the producer and personnel. 7. Permanent consultancy via Internet. 8. Entailment of the productive chain with universities. The farm has 105 cows and 80 heifers of Holstein breed. The cattle were confined, AI was used and their feeding was with corn silage, alfalfa and concentrates. It has advisory services as well. The results were: a) Actualization programs in five areas given to the adviser. b) Problems identified by the diagnosis (initial value) and monitor progress with the SPRP (final value): Age at first parturition (25.47 - 24.68 m), parturition-first service interval (80.82 - 75.39 d), parturition-conception interval (134.16 - 108.65 d), conception rate (41.74 - 48.24 %), milk production average (21.40 - 22.27 L), days in production (353 - 357), dry days (63.41 - 59.83); c) Elaboration of an organizational chart and a procedures manual. d) Training programs in three areas given to the personnel. e) Evaluation of the adviser performance considering farm progress. f) Involvement of a student and professors in the work. The advisory model improved the productive performance, administrative process and personnel attitude; the latter was the most important for the solution of the main problems. The use of a digitized platform by the producer, adviser and consultant facilitates the farms development. [ABSTRACT FROM AUTHOR]