Source of the information

The information analyzed was taken from databases belonging to 17 dairy agribusinesses, located in the southern part of the region of the Jalisco Highlands. The information was captured by technicians advising the agribusinesses in the study, through the AGROPEC-Star^® software, which is a tool for the management of agribusinesses. The information used was taken from the global report that the software generates, which was then exported to the Microsoft Excel^® software to be edited.

Agribusinesses

The agribusinesses considered correspond to two levels of stratification: entrepreneurial and transition, according to the classification by ^{FAO (2005)} modified by ^{López et al. (2007)} and adapted for the study region, including only the two technological levels cited out of the five that FAO considers.

Entrepreneurial technological level: the producers from entrepreneurial agribusinesses have an average schooling of undergraduate level; they all own rainfed agricultural surface and 50 % have pastureland; from the livestock herd, they sell the male offspring as soon as possible, keeping the females for replacement; they have in average 190 heads of livestock and the cows are serviced only via artificial insemination; the diet is based on cut fodder and balanced meals; in some cases, this diet is offered depending on the physiological state and the level of production in a feedlot system.

Transition technological level: the producers of transition agribusinesses have an average schooling level of secondary; 73 % of them own a surface of agricultural use or rainfed prairie; 13 % with agricultural surface or irrigation prairie; and 53 % with pasturelands of good quality. They have in average 87 heads of livestock and within the reproductive management they apply artificial insemination and mounting for those animals that were not pregnant after the insemination; the diet of the livestock is variable, and it is performed by grazing cultivated prairies or pasturelands plus balanced meals and a mineral supplement in a semi-feedlot system, or else, in feedlot systems based on cut fodder and balanced meals, but without the diet being differentiated by physiological stage or level of production.

The genetic quality of the dairy herds of both strata of producers is similar, constituted mainly by livestock of the Holstein breed. The adoption of management and health practices, as well as the infrastructure and equipment, is greater in the entrepreneurial level than in the transition one. Considering the differences in the characteristics of agribusinesses it is suggested that the reproductive behavior of the two types of ranches is different.

Databases

The database was constituted by 17 agribusinesses, of which 15 are transition, with 1441 cows, and two entrepreneurial ones, with 600 cows; this is a total of 2041 cows with 1 to 13 labors taking place between 1996 and 2008. The numbers of labors equal or greater than seven were classified as labor seven, with the aim of eliminating the effect of the lost cells. A distribution graph of the values generated was obtained for the variables studied, which were age at first labor (AFL), services per conception (SPC), open days (OD), interval between labors (IBL), interval to first post-partum heat (IFPH), and interval to first post-partum service (IFPS); and the data that were biologically not probable were eliminated, such as the case of the variable open days, where those that were lower than 21 days were eliminated. Due to insufficient records for the variables "services per conception" and "interval to first post-partum service", the data from two agribusinesses classified in the transition technological level were eliminated, and one for the variables interval between labors and interval to first post-partum heat.

Statistical analysis

For the analysis of the variables, a mixed model was considered which included the fixed effects of number, year and season of labor, technological level and ranch, in addition to the double interactions between these, which had a significant effect (p≤0.05). For the variable age at first labor, the year of birth is used instead of the year of labor. Likewise, the agribusiness nested within technological level and cow nested within agribusiness and technological level were considered as random effect. The model is presented next:

Y _ijklmno = μ + NT _i + EP _j + NP _k + AP _l + AE(NT)_m + V(AE)_n + (APxNT)_li + (APxEP)_lj + (NPxAP)_kl + (NPxEP)_kj + e _ijklmno

where: Y _ijklmno: response in each one of the response variables modelled, μ: general mean, NT _i: effect of the i-th technological level (i= 1 = transition, i = 2 = entrepreneurial), EP _j: effect of the j-th season of the labor [j = 1 = dry (June-October), j = 2 = rain (November-May)], NP _k: effect of the k-th number of labor (k=1, 2, 3, 4, 5, 6, 7 or more), AP _l: effect of the l-th year of labor (l= 1996, ...2006 or more), AE(NT)_m: random effect of the m-th agribusiness (m= 1, T..17) nested in NT~N (0, σ ²a), V(AE)_n: random effect of the n-th cow (n=1, ...2041) nested in AE~N (0, σ ²v), (APxNT)_li: effect of the interaction of the l-th year of labor with the i-th technological level, (APxEP)_lj: effect of the interaction of the l-th year of labor with the j-th season of labor, (NPxAP)_kl: effect of the k-th interaction of the number of labor with the l-th year of labor, (NPxEP)_kj: effect of the interaction of the k-th number of labor with the j-th season of labor, e _ijklmno: random effect associated with each observation ~N(0, σ ² e).

The reproductive indicators are analyzed with the MIXED procedure from ^{SAS (2013)} and the REML method was used. In order to obtain the measurements of the minimum squares of the principal effects and the interactions, the LSMEANS formulation was applied. For the means comparison of the minimum squares, the adjusted Tukey test was used (^{Kramer, 1956}).

Age at first labor (AFL)

The intervals of the effect of the interaction between year of birth and technological level are presented in Figure 1, where the cows of entrepreneurial technological level presented a minimum of one month less of age at first labor in 45 % of the years graphed, compared with the cows of the herds with transition technological level.

Figure 1 Interaction between year of labor and technological level for the age at first labor in agribusinesses of entrepreneurial (■) and transition (○) type. 

The entrepreneurial technological level presented an average of 25.2±0.8 months of AFL and in the transition, 26.1 ± 0.3 months, which indicates that the agribusinesses of both technological levels do not enter the optimum reported by ^{Medina (2003)} and ^{Córdova et al. (2005)}, who report values between 22 and 24 months in feedlot dairy ranches; however, they are also not indicators of problems because they are outside the range of <24 or >30 months. Although there weren't significant differences, the cows of the entrepreneurial ranches do reach optimal values of AFL, while those of the transition agribusinesses do not, which shows that in the entrepreneurial herds there is a tendency to manage replacement females in the most adequate way. It is considered that improving the dietary management (^{Friggens et al., 2010}) and the detection of heats (^{Lane et al. , 2013}), the AFL can be optimized by both types of agribusinesses.

Interval to first post-partum heat (IFPH)

In Figure 2, the results of the interaction between year of labor and technological level for the interval to first post-partum heat were presented, where the magnitude of the differences of IFPH between technological levels turned out to be greater in 2004 and 2007. The entrepreneurial technological level presented 27 d less in average of interval to first post-partum heat compared to the transition level, for it reached an average level of 63.8 ±6.2 vs 90.8 ±2.7 d of the transition level, possibly due to a better detection of heat and a more adequate dietary management in the agribusinesses of entrepreneurial type. However, the herds classified in both technological levels are far from the optimum reported by ^{Ortiz et al. (2005)} in dairy cattle managed intensively, who indicate that it must be under 40 d, since, according to ^{Linderoth (2005}), the presentation of heats at 40 d are an indication that the cows in these production systems are cycling normally and can respond adequately to the insemination protocol. According to ^{Friggens et al. (2010}), there is a close relation between the reproductive yield and milk production, which is why the cows that take longer in returning to estrus after labor have lower conception rates and show less signs of estrus. This could be related to a higher milk production, which is why it is important to implement nutritional strategies to provide an adequate diet according to the level of production of the cow and to try to minimize a negative effect in its reproduction, which can be measured with body fat as an index of capacity to safeguard the reproductive investment and the mobilization of body fat as an index of the current nutritional environment.

Figure 2 Interaction between year of labor and technological level for the interval to first post-partum heat of agribusinesses of entrepreneurial (■) and transition (○) type. 

Interval to first post-partum service (IFPS)

Figure 3 shows the results of the interaction between year of labor and technological level for the interval to first post-partum service, where the magnitude of the differences in IFPS between technological levels was greater in 2004, 2005 and 2006. The entrepreneurial level presented, in average, 15 days less for the interval to first post-partum service than the transition level.

Figure 3 Interaction between year of labor and technological level for the interval to first post-partum service of agribusinesses of entrepreneurial (■) and transition (○) type. 

The entrepreneurial technological level was better than the transition one since it presented lower IFPS (75.5±5.5 vs 91.1 ±2.3 d), being the reflection of what was obtained for the IFPH.

^{Arbel et al. (2001}) mention that a delay of 60 days with regards to the period of voluntary wait in insemination of the high-producing cows brings economic advantages and allows the producer to make decisions regarding each cow. ^{Miller et al. (2007}) report that a period of voluntary wait of 60 days equal to the days until conception, is assumed to calculate the pregnancy rate (^{De Jarnette et al., 2007}).

^{Stewart and Rapnicki (2006}) mention that in this analysis, high-producing cows are those of second and third labor for which an interval to first service of 84.5 ±3.1 and 81.7±3.1 d was found. However, ^{Ramírez and Segura (1992)} reported 83 d of IFPS for dairy cows in intensive systems of northeastern México. ^{Nebel (2003}) recommends as goal 75 d at first service in systems of intensive production, and ^{Córdova et al. (2005)} published an optimum of 77.53 d in cows of feedlot dairy production. According to this analysis, the entrepreneurial producers obtained a mean of 75.7± 5.5 d of IFPS and the transition ones of 91.1 ± 2.3 d, so it is deduced that the entrepreneurial producers present a more adequate IFPS than the transition producers in the biological aspect.

In Table 2, the minimum square means of the principal effects for the reproductive variables analyzed are presented.

The general AFL mean was 25.7±0.6 months; the values for the IFPH and IFPS were 77.35 ±3.48 and 83.41 ±3.33 d, and 125.14±7.14 d for OD. ^{Marini et al. (2004}) compared cows of 26.1 ± 0.02 and 36.6± 0.13 months of AFL and found that Holstein cows with 26.1 months of age presented a greater interval to first post-partum heat (76.1 ±1.99 d), at first post-partum service (122.8±3.84 d) and longer periods of open days (140.3±3.97 d) than those of 36.6 months of age. On the other hand, ^{Nilforooshan and Edriss (2004}) mention that 24 months is the ideal age at first labor. When comparing the results from this study to those found by ^{Marini et al. (2004)}, it can be observed that AFL and IFPH were similar; however the IFPS and OD were 39 and 15 d shorter than those found by the authors mentioned, indicating that the general management of the agribusinesses under study is good, because the productive life of the cow begins at an age close to that recommended by ^{Nilforooshan and Edriss (2004)}, with shorter intervals to post-partum service and, as a result of this, less open days, factor that translates into less economic losses attributed to feeding costs, salubriousness and labor, primarily.

The cows of first labor presented more days (p≤0.05) at first post-partum heat (84.3±3.5 d) and first post-partum service (86.9±3.1 d) than those of three and four labors; the latter presented less days of IFPH (73.8±3.7 and 71.0±3.8 d), and IFPS (81.7±3.1 and 79.8±3.2 d), which agrees with the results reported by ^{González (2008)}, who mentions that cows of first labor receive their first post-partum service days later than those of third and fourth labor.

The entrepreneurial technological level presented less days (p≤ 0.05) of IFPH and IFPS (63.8± 6.2 and 75.7±5.5 d) than those of transition (90.8±2.7 and 91.1 ±2.3 d). In this regard, ^{Hillers et al. (1984}) reported that factors related to management could influence directly the reproductive behavior of the dairy herd, among them: timely detection of heats, adequate management of the semen, insemination techniques, salubriousness, genetic improvement, and diet of the cow. Likewise, ^{Lane et al. (2013}) indicate that the reproductive behavior is the result of the action of various factors, which is why ^{Overton and Waldron (2004}) mention that it is necessary to achieve the optimal nutrition of the cow, whose requirements vary according to the physiological status, in addition to satisfying the specific nutritional demands during the dry period to prevent metabolic disorders during the perinatal period; therefore, it can be considered that the nutritional management of the cows in the entrepreneurial system is more adequate (perhaps not optimal), and also that the better management in the detection of heats than in the transition systems, for they have different rations according to the physiological stage of the cow and they are confined. Therefore, they present a better response to the variable of IFPS.

Open days (OD)

According to what is shown in Table 2, the entrepreneurial technological level presented an average of 119.3± 11.5 open days and of 131 ± 4.9 d for the transition, without there being a statistical difference between them. ^{Ortiz et al. (2005)} point out an optimum of 85 to 110 open days, with figures over 140 d as indicators of problems in intensive systems, which are similar values to the optimum ones reported by ^{Córdova et al. (2005)} of 85 to 100 OD in a feedlot system. In this study, a general average of 125 OD was obtained, indicating that the agribusinesses have an adequate period of OD. The agribusinesses with entrepreneurial technological level presented 11.7 OD in average, less than in those of transition, but this difference was not significant (p≥0.059).

Services per conception (SPC)

The number of labor influenced the services per conception (Table 2); the SPC are increased gradually with the age of the cows. For the first partum cows the number of services per conception was 1.68± 0.1, less than for those of seven or more (2.16± 0.1). ^{Hillers et al. (1984}) mention that there are many factors that influence the reproductive behavior of dairy cows and which have great impact on fertility, among them, the number of labor and the age; concerning the latter, they report that those of one and two labors have a better percentage of conception than those of three or more.

Agribusinesses with entrepreneurial and transition technological level presented 2.04± 0.2 and 1.72 ±0.1 SPC. ^{Ortiz et al. (2005)} point out an optimum under 1.7 SPC and as indicator of reproductive problems, more than 2.5 SPC, which is why the agribusinesses in study are found within the range of acceptable values.

During rainy season there were fewer services per conception than during the dry season, while the IFPH and IFPS were lower for the latter. ^{Maciel and Scandolo (2008}) mention that the intense rains reduce the estrum activity and the manifestation of heats in climates with environmental temperatures over 30 °C and rain; it is three times less notorious than in the dry climate with temperatures of 20 to 25 °C.

The fact that during the dry season the signs of estrum behavior can be observed better has an influence on the early start of the detection of heats and insemination; such an event agrees with the results found in this study. On the other hand, the fact that fewer services per conception take place during the rainy season could be related to the fact that in such a period the nutritional quality of the fodder that is offered to the cattle is better and, therefore, the reproductive activity also, for it is well-known that the reproductive behavior is closely associated to the nutritional status.

Interval between labors (IBL)

The technological level (p>0.05) did not influence the IBL, which agrees to what was reported by ^{Caldera (2003)} in agribusinesses with low, medium and high technological levels in the region of the Jalisco Highlands. In this analysis of the sources of variation included, only the year of labor had an effect on the IBL. A mean of 396.7±11.1 d (13.22 months) of IBL was found for the entrepreneurial producers and of 406.9 ±4.9 d (13.56 months) for the transition ones. ^{Teyer et al. (2002)} reported 15.6 months of interval between labors in specialized dairy systems from southern México. ^{Córdova et al. (2005)} mentioned an optimum of 12 months of IBL in feedlot systems, quite similar to that reported in intensive systems by ^{Ortiz et al. (2005)} of 12.5 to 13 months, with 14 months as indicator of problems; however, in cows with a similar production system, ^{Nebel (2003}) recorded an optimum of 13.5 months of IBL. According to the literature cited, the agribusinesses studied are within the recommended values.

The general average of interval between labors was 401.8 days, similar to the 406.8 days reported by ^{Hare et al. (2006}) for Holstein cows in intensive systems.

Based on the results obtained, it is identified that there are only differences in the IFPH and IFPS, and that the cows from agribusinesses of the entrepreneurial TL have a better behavior up until the 60 days after labor, since they present heat and are inseminated sooner. However, these differences are not as important to have an impact on the indicators of OD and IBL, since at the end the animals from different technological TLs have a similar reproductive behavior.

In addition, in future studies it is important to analyze whether the difference in investment that there is in infrastructure and livestock is significant in the two technological levels to have more elements to identify the most profitable one.