Reproductive performance of dual-purpose cows
in Yucatan, México

  Mario Osorio-Arce and José Segura-Correa* 

Colegio de Postgraduados, Campus Tabasco, Mexico
* Facultad de Medicina Veterinaria y Zootecnia Universidad Autónoma de Yucatán, Mexico

Abstract

A transversal study was carried out with the objective to know the reproductive status of dual-purpose cattle and to determine the effect of some environmental and breed group factors on the proportion of cows found pregnant (PCP) and calving to conception interval (CCI) in Yucatan, Mexico. The climate of the region is tropical sub-humid with monthly temperature and annual rainfall averages of 26 C and 1100 mm respectively. Main characteristics of the dual-purpose herds in south-eastern Mexico are: milking of cows once a day with calf at foot; the use of crossed Brown Swiss x Zebu or Holstein x Zebu cows, fed mainly on pastures and the use of rustic infrastructure. A team of veterinarians conducted the diagnosis from November 1996 to December 1999. A total of 5133 rectal palpations from 162 herds of a total of 340 herds were obtained. PCP data were analysed using Chi-square test and CCI data by time-event procedures.

Fifty one percent of the cows palpated were pregnant. Of the non-pregnant cows, 35.3% were cycling. Statistical differences in PCP were found among zones, seasons of calving and breed groups. The east zone had the highest PCP (52.5%) followed by the south zone (49.8%). The dry season had the highest PCP (58.5%) and the worst corresponded to the rainy season (31.9%). Crossed Brown Swiss x Zebu and Holstein x Zebu cows had a higher PCP than the pure Brown Swiss or Holstein cows, although they were similar to the Zebu cows. CCI mean was 183+5.6 days. The probabilities that a cow gets pregnant at 4 or 6 months postpartum were 18.4 and 31.8%, respectively. The probability of an CCI of 180 days or less was lower for the crossed cows (Bos taurus x Bos indicus) compared to the Brown Swiss and Holstein cows. 

Keywords: dual purpose cattle, reproduction, Mexico

Resumen 

Se realizó un estudio transversal con el objetivo de diagnosticar el estado reproductivo de vacas de doble propósito, así como determinar el efecto de algunos factores ambientales y genéticos en el porcentaje de vacas encontradas preñadas (PVP) e intervalo parto concepción (IPC) en el estado de Yucatán, México. El clima de la región es tropical subhúmedo con promedios de temperatura mensual y precipitación anual de 26 C y 1100 mm, respectivamente. Las características de los hatos de doble propósito en el sureste de México son: la ordeña una vez al día con apoyo de la cría, vacas generalmente cruzas de Suizo x Cebú o Holstein x Cebú, el alimento básico son los pastos y las instalaciones son rústicas. Un equipo de médicos veterinarios especialistas en diagnóstico de preñez realizaron los exámenes en las vacas de noviembre de 1996 a diciembre de1999. Un total de 5133 palpaciones en 162 hatos, de un total de 340 fueron obtenidas. Los datos del diagnóstico reproductivo se analizaron por pruebas de Chi-cuadrado y los de IPC a través de procedimientos evento-tiempo. El 51.2% de las vacas se encontraban gestantes. Del total de vacas vacías, el 64.7% estaban estáticas y el 35.3% estaban ciclando. Se encontró diferencia entre zonas, épocas de parto y grupo genético en el PVP. La zona Oriente tuvo los mayores PVP (52.5%), seguida por la zona Sur (49.8%). Asimismo, los mayores PVP correspondieron a la época de seca (58.5%) y los menores a la época lluviosa (31.9%). Las vacas cruzadas Suizo x Cebú y Holstein x Cebú, tuvieron mayores PVP que los grupos Suizo Pardo o Holstein puros, aunque fueron similares a las vacas Cebú. La media aritmética del IPC fue 183+5.6 días. Las probabilidades de una vaca gestante a los 4 o 6 meses postparto fueron del 18.4 y 31.8%, respectivamente. La probabilidad de un IPC menor de 180 días fue mayor para las vacas cruzadas (Bos taurus x Bos indicus) en comparación con las vacas Suizo Pardo y Holstein puras. 

Palabras claves: ganado de doble proposito, reproducción

Introduction 

Reproductive performance is one of the chief components that determine the economic efficiency of an animal or the whole herd. Fertility of the herd is crucial to obtain replacements and milk production for the calf or for human consumption (Voh and Otchere 1989; Villa-Godoy and Arreguin 1993). Therefore, an important starting point in any program to improve productivity is to evaluate the reproductive performance of the herds. There is little information on the reproductive aspects of dual-purpose cattle in Mexico and particularly in the state of Yucatan, at experimental level and under commercial conditions. Available information is based normally on survey results from questionnaires (Segura 1980; Anderson et al 1992). However, questionnaires have their own limitations, especially when there are no records of the events and producers notify by memory. Therefore the results from the physical examination of cows, by experienced people,  must be more precise than those obtained by questionnaires. 

The objectives of the present study were to diagnosis the reproductive status of dual-purpose cows, and to determine the effect of some environmental and breed group effects on the percentage of cows found pregnant and calving to conception interval of dual-purpose herds in Yucatan, Mexico..

Materials and methods 

The study was carried out in 162 herds of a total of 340 herds located in the state of Yucatan, Mexico, from November 1996 to December 1999. The climate of the region is sub-humid tropical, with a summer rainy season. The monthly maximum temperature varies between 35 C and 40 C, the mean temperature being 26.6 C. The relative humidity varies from 65 to 100% (mean 78%) and annual rainfall varies from 415 to 1290 mm, depending on the area (INEGI 1994).  

Yucatan is classified into three regions according to type of vegetation and agricultural development: the sisal region (centre-northern) dedicated mainly to the exploitation of sisal (Agave fourcroydes), the agricultural region (southern) with main activity the production of maize and citrus; and the livestock region (eastern) where 65% of the cattle of the state is concentrated (INEGI 1994). The predominant livestock production system is semi-intensive (beef farms), mainly based on year-round grazing on improved pastures, commonly Guinea grass (Panicum maximum) and Star grass (Cynodon nlemfuensis), with supplementary feeding during the dry season.  

The general management of the herds is based on the milking of crossbred cows, mainly Holstein x Zebu or Brown Swiss x Zebu cows, once a day with the calf at foot. A team of veterinarians with experience in reproductive diagnosis made the transrectal palpations of 5133 cows. Of these cows only 2901 had the breed group identified and had a calving date. Therefore for the comparison of breed groups only 2901 data were used. 

The calving to conception interval (CCI) for the pregnant cows was obtained as the difference in days between the diagnosis date and the previous calving date, minus the number of days the cow was pregnant. Information on the empty cows was obtained as the difference in days, between the date of diagnosis and the date of the previous calving (censored data). Censored data for CCI with less than 46 days were eliminated. Data on reproductive status (pregnant or empty) of cows were analysed by Chi-square tests and those on CCI were processed using event-time type analysis. Months of diagnosis were grouped in three seasons according to the climate: dry season (February to May), rainy season (June to September) and windy and rainy season (October to January). Differences between genetic groups in the distribution probabilities of CCI were tested using Wilcoxon rank test. All statistical analysis were computed using the SAS program (SAS 1996). 

Results and discussion 

Proportion of cows found pregnant 

Of the 5133 cows examinated, 2630 were pregnant (51.2%) and 2503 empty (48.8%). This percentage are similar to the birth rate of 53.0% found in the Llanos of Colombia for beef cattle (Stonaker et al 1976); but greater than the pregnant rate (41.9%) notified in Nigeria by Voh and Otchere (1989). According to Plasse (1987) the pregnant rate in beef cattle herds is less than 50%. This low reproductive level is the result of the direct and indirect action of many environmental factors that affect the physiological systems of the cattle, altering its growth, lactation and reproduction. Among the main limiting factors figure the high temperature-humidity indexes and seasonality of the rain which provoke variation in the quantity and quality of grass, incidence of parasites, and inadequate management of the herds, because of lack of practical information for the producers of their own production system (Frisch et al 1987).  

Of the 2503 empty cows, 919 were cycling (35.3%) and 1684 were static (64.7%). The results of this study agree with those observed by Delgado (2000) in a beef cattle herd, examined at 120 days postpartum. Delgado (2000) found that 62.9% of the cows were empty; of which 37.0% were cycling and the rest 63.0% were in true anoestrus. The incidence of anoestrus in this study is similar to that reported by Wells et al (1986) in Africa with Bos indicus cattle. They found that 40.0% of the cows were in anoestrus at 100 days postpartum. However, other studies carried out in beef cattle in other tropical regions reported percentages of anoestrus postpartum higher than those found in this study; for example, Gyawu (1988) obtained an incidence of anoestrus of 50 % for all the cows examinated 9 months after calving. Similarly, Bolaños et al (1996) reported that 65% of the cows did not return to ovarian activity 126 days after calving. This result agrees with those of Mukasa–Mugerwa et al (1991), who reported that 63.1% of the cows were in true anoestrus after five months of lactation. However, Corro et al (1999) in dual-purpose herds in Veracruz, Mexico, reported that 65% of the cows were cycling. 

Factors affecting the proportion of cows found pregnant (PCP)

Zone, season of diagnosis and breed group had significant effects on PCP (P<0.05). The eastern zone had the highest PCP (52.5%), followed by the southern (49.8%) and central zone (44.0%). Differences among zones could be attributed to differences in management practices, status of the paddocks, farm size and breed group used in each zone (Osorio-Arce et al 1999). 

Due to the seasonality of forage production there is a trend to a highest conception rate from July to October, with a calving season from April to July. Given a 90 to 120 days period of anoestrus it is expected a high PCP at the beginning of the windy and rainy and in the dry seasons when parities started. In this study, the highest proportion of pregnant cows corresponded to cows examined in the dry season (58.5%), followed for those examined in the windy and rainy (51.5%) and rainy (31.9%) seasons. The results of this cross-sectional study disagree from those of the prospective study by Delgado (2000), in a herd in Yucatan, who found a higher probability of pregnancy in cows calving in the windy and rainy season compared with the dry and rainy seasons. The low PCP found in the rainy season could be associated, in part, to the fact that in this season occur most of the calvings, and therefore the cows are empty. 

The breed groups Brown Swiss x Zebu and Holstein x Zebu, had higher PCP than the pure breed group cows (Brown Swiss or Holstein), although they were similar to the Zebu breed group (Table 1). Studies done on fertility of beef cattle comparing crossbred F1 cows, suggested that crossbred animals are superior to Zebu (Madalena and Hinojosa 1976; Larson et al 1984; Osoro 1986). The superiority of crossbred animals is attributed to the effect of heterosis or to a greater adaptation of Bos indicus x Bos taurus crosses under those environmental management conditions (MacKinnon et al 1989; Taneja and Bhat 1986; Madalena et al 1990). 

Calving to conception interval 

The arithmetic mean for CCI was 184+5.6 days, which is greater than the means of 160 and 167 days notified for dual-purpose cattle in Veracruz, Mexico (Corro et al 1999) and Latin-America (Vaccaro 1986), respectively. However, it is similar to that obtained by Leme de Magalhaes-Labarthe (2001) in dual-purpose cattle at an experimental centre in Veracruz (178 days). 

The general probabilities of a pregnant cow at 4, 6 or 8 months after calving were: 18.4, 31.8 and 47.2%, respectively. That means that only 18.4% of the cows get pregnant 120 days after calving, which is the time required to have a calf every 13 to 14 months. This value is lower than those obtained in beef cattle by Aban et al (2002) and Delgado (2000) in Yucatan (40.0 and 37.1%, respectively). These authors signalled that body score and change of body score after calving are one of the main factors affecting CCI. 

The probability distribution functions for the five breed groups were different (P<0.01) and are given in Figure 1. As can be appreciated the probability distributions were similar for the Brown Swiss x Zebu and Holstein x Zebu cows, but different with respect to the other breed groups studied. The CCI median for the Brown Swiss cows was not obtained, because only 35.8% of the cows of this breed group got pregnant. The CCI medians for Holstein, Brown Swiss x Zebu, Holstein x Zebu and Zebu were: 244, 204, 184 y 205, days, respectively. 

Conclusion  

The percentage of cows found pregnant in the dual-purpose herds in Yucatan, Mexico was low; however, it is within the range of values reported in the literature for tropical regions. Region, season and breed group affect the percentage of pregnant cows. The CCI medians obtained in this study were large, with differences among breed groups. Therefore, better management practices and the use of appropriated Bos taurus x Bos indicus breed groups could improve the reproductive performance of cattle in Yucatan, Mexico. 

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 Received 15 June 2002

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