Beef cattle breeding has developed in extensive grazing systems in Mexico, concerning the livelihood of over one million families and affecting the use of natural resources. Reproductive efficiency is a major determinant of both the environmental impact of the herd, and the economic viability of the cow-calf production system. However, as reproductive traits have low heritability, reproductive efficiency can be largely influenced by herd management practices. Thus, a questionnaire was administered as personal interviews to 3280 producers, to investigate the prevalence of practices that could directly influence the reproductive outcome of their cattle. Results show that year-round breeding (93%) and natural service by the bull (97.4%) are the most common mating methods. However, only 41% of producers evaluate the breeding soundness of their bulls, and diagnostic testing for specific reproductive diseases of the sires is barely performed in 20% of the farms. The main declared reason for replacing the bull is old age (26.8%), which is followed by to avoid inbreeding (68.4%). Less than 10% of the operations use methods for the synchronization of the estrous cycle, and most farmers breed their heifers for the first time after 2 years of age (73%). Diagnosis of pregnancy is performed in merely 31% of operations, with 23% of the producers declaring to discard non-pregnant cows. Energy or protein feed supplements are provided to the cattle in 63% of the production units, whilst mineral supplements are given in 79% of the farms. Calves are typically weaned between 6 months and a year of age (85%). Only 16% of operations vaccinate against brucellosis and 17.5% against other reproductive diseases (IBR-DVB-VSR and Leptospirosis). The present study showcases a low frequency of adoption of basic reproductive management practices by cow-calf operations in Mexico. Advancement of these practices, as well as implementation and promotion of associated technologies, denotes an area of opportunity to improve the reproductive efficiency of the national herd.

The aim of this study was to determine whether increasing concentrate supplementation to ewes during the peripartum would benefit ewe and lamb vigour. Pregnant ewes were randomly assigned to either a maintenance group (MG) or a supplementation group (SG). The diets given covered energy requirements and consisted of pasture, forages and commercial concentrate; however, SG ewes received higher concentrate ration. Body weight and blood metabolites were assessed weekly. Lambs were weighed and their behaviour was observed. Data were analysed using repeated-measures test or ANOVA. During peripartum, the body weight was significantly higher in SG ewes compared with MG ewes (P = .02). Indicators of energy metabolism were similar between groups (P > .05). Latency to first suck was 10 minutes shorter in SG lambs compared with MG lambs (P = .005). Lamb weight was similar between groups, and there was a negative correlation between lamb birthweight and time to first suckle that was independent of diet group. This study demonstrates that high concentrate supplementation of ewes during peripartum results in higher body weight postpartum but does not change metabolic status. Latency to first suck was shorter in lambs born to SG ewes suggestive of enhanced vigour related to supplementation.

We determined whether sheep discriminate among different mineral supplements containing P and Mg and if they modify their selection as a function of the basal diet received. Forty lambs were offered four-way choices among inorganic sources of P and Mg: magnesium oxide in its coarse 1) C-MgO and granular 2) MgO forms and magnesium phosphate: 3) Mag33 (33% Mg and 2.7% P), and 4) MGP (25% Mg and 15% P), and two-way choices between MGP and each of the other minerals, and between MgO and C-MgO (baseline). Subsequently, lambs were randomly assigned to four groups (10 lambs/group) and fed rations such that the levels of Mg and P were low (LMg_LP), adequate (NMg_NP), low in Mg and adequate in P (LMg_NP), or adequate in Mg and low in P (NMg_LP). After 29 d, choice tests (post-deficiency) were repeated. During baseline, lambs ate and preferred Mag33 > C-MgO = MGP > MgO (P < 0.05). This pattern remained during post-deficiency tests, but lambs in LMg_LP and LMg_NP increased their preference for MGP and C-MgO, respectively, whereas lambs in NMg_LP increased their preference for C-MgO and MGP relative to baseline (P < 0.05). The serum concentrations of P and Mg increased after preference tests, and preference for MgO and MGP in low-Mg groups increased as the serum concentration of Mg declined (P < 0.05). Thus, lambs discriminated among different minerals and some groups modified their preferences based on the basal diets received, which rectified mineral imbalances.