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Objective. To characterize growth curves and reproductive performance of Romosinuano cows in Mexico. Materials and methods. Weight and age records (928) of females (117) for growth traits and calving records (459) of cows (113) for reproductive traits were analyzed. Four non-linear mixed models were adjusted to describe the growth curves. Indicators of age at 50% of maturity A50M), and percentage of maturity at 18 months of age (PM18) were estimated. The reproductive performance was evaluated through the age at first calving (AFC), the calving interval (CI), and calving rate (CR). Results. The Brody model showed the best adjustment to the growth curve. The A parameter, which estimates maturity weight, fluctuated within 430.2 and 466.2 kg; the b parameter within 0.94 and 5.45; and the k parameter within 0.001 and 0.002; depending on the used model. The A50M varied from 20 to 21 months, and the PM18 from 44.5 to 45.5%. The means for AFC, CI, and CR at 550 d were 1059±282 d, 553±68 d, and 74±19%; those indicators improved (p<0.05) when cows have a higher percentage of their maturity weight, depending on calving season. Conclusions. The estimates of maturity weight indicate that Romosinuano cattle could be considered as a breed of small or medium size, with an acceptable reproductive ability. The females with small estimated maturity size aged at first calving earlier than cows with high weights. [ABSTRACT FROM AUTHOR]

The objective of the present study was to evaluate some environmental factors on the reproductive performance of an Angus herd under grassing conditions in the Mexican Bajio. Data of a pure breeding exploitation of the municipality of Leon, Guanajuato were used. The region has a temperate sub-humid climate with rains in summer; the animals used were fed in a free range pasture. Breeding takes place during two periods, one from May to July and another from December to January and weaning occurs approximately at seven months of age. The data were analyzed using the method of least square to determine the effect of parity year (PY= 1991-2007), parity season (PS = cold: December-March; dry: April-June; and rain: July-November), and parity number (PN = 1, 2,…≥9). The response variables studied were age at fist calving (AFC), and calving interval (CI). The overall means and standard deviations for AFC and CI were 793.5 ± 165.8 and 407.5 ± 83.5 days. The PY, PS and PN affected (P < 0.01) the CI. From these results it might be concluded that the year, season and parity number are important in the reproductive performance of the Angus cows under range management conditions. [ABSTRACT FROM AUTHOR]

Pedigree and reproductive records of 151 Brown Swiss cows were analyzed with the objective of estimating the heritability (h2) and the repeatability (r) for different measures of fertility. Cows were daughters of 49 sires and 102 dams. The study was carried out at Las Margaritas research station located in Puebla, Mexico. The pedigree was the same for all traits; it consisted of 287 individuals, and included dams without records and sires. Genetic parameters were estimated for conception rate at first service (CR), days to first registered heat after calving (OH), days to first registered service after calving (DS), days open (DO), and calving interval (CI). Estimations were made independently for each trait with a repeatability animal model, which included the direct additive genetic effect, as well as the permanent environmental effect of the cow. Genetic parameters were estimated with restricted maximum likelihood. In general, estimates of permanent environmental variance were greater than estimates of additive genetic variance, so that r was mainly determined by permanent environmental effects. Estimates of h2 and were: 0.02 ±0.06 and 0.16, 0.00 ± 0.05 and 0.15, 0.03 ± 0.03 and 0.03, 0.00 ± 0.03 and 0.14,and 0.03 ± 0.07 and 0.12 for DH, OS, CR, DO and CI. Artificial selection as a tool to induce genetic change in measures of fertility studied would be slightly effective because additive genetic variance is scarce. [ABSTRACT FROM AUTHOR]

The article discusses research which analyzed the calving interval (CI) and birth weights (BW) of Zebu cows to determine the effect of some environmental and breed factors on CI and BW and estimate repeatability in a herd from eastern Yucatan, Mexico. Statistical data were taken to document the means of least squares for CI of Zebu cows and BW of the calves. It suggests that the reproductive performance of the Zebu cows can improve through the use of Nelore cows and the substitution of the Indubrazil breed.

A total of 1338 high-yielding cows with five lactations from a large well-managed commercial dairy operation in a hot environment of northern Mexico were used to evaluate milk yield and reproductive performance of cows undergoing unplanned extended lactations (EL; > 450 days). The null hypothesis that cumulative milk yield during five consecutive lactations is the same in cows not having unplanned EL and cows with several EL was tested. All EL resulted from cows failing to become pregnant with ≥ 4 services. Cows were allocated to 1 of 6 groups according to the number of EL (EL0 for cows with no EL to EL5 for cows with 5 EL). Cumulative milk yield was highest (P < 0.01) for EL5 cows (95,499 kg) and lowest for EL0 cows (56,236 kg). Likewise, cumulative days in milk were greatest (P < 0.01) in EL5 (2968 days) and lowest in EL0 (1857 days) cows. Mean milk yield per lactation increased linearly with the increase in the number of extended lactations with a maximum of 19,099 kg of milk/lactation for EL5 cows. Mean daily milk yield/productive life was lowest (P < 0.01) for EL0 (30.2 kg) and highest for EL5 (32.1 kg). The percentage of days in milk relative to days from birth to the end of the fifth lactation was highest for EL5 (78.1%) and lowest for EL0 (59.6%), with EL2 to EL4 cows intermediate. Length of calving interval was longest (P < 0.01) for EL5 (24.7 months) and shortest for EL0 (15.5 months) cows. It was concluded that it is worthwhile maintaining high-yielding cows incapable to conceive before 230 days in milk because they did conceive again and produced considerable amounts of milk during their productive life, which substantially prolonged their permanence time in the herd.