Records representing data from 1,500 barren Holstein cows over an 8-yr period from a large commercial dairy farm in northern Mexico were analyzed to determine the effects of lactation number and season and year of initiation of lactation on milk production of cows induced hormonally into lactation and treated with recombinant bovine somatotropin (rbST) throughout lactation. Peak and 305-d milk yields were also assessed as predictors of total milk yield in cows induced into lactation. A significant quadratic relationship was found between 305-d milk yield and number of lactation [7,607±145 and 9,548±181 kg for first- and ≥6-lactation cows, respectively; mean ± standard error of the mean (SEM)] with the highest production occurring in the fifth lactation. Total milk yields of cows with ≤2 lactations were approximately 4,500 kg less than milk yields of adult cows (the overall average ± standard milk yield was 13,544±5,491 kg per lactation and the average lactation length was 454±154 d). Moreover, 305-d milk production was depressed in cows induced into lactation in spring (8,804±153 kg; mean ± SEM) and summer (8,724±163 kg) than in fall (9,079±151 kg) and winter (9,085±143 kg). Partial regression coefficients for 305-d milk yield and peak milk yield indicated an increment of 157 kg of milk per lactation per 1-kg increase in peak milk yield (r(2)=0.69). Neither peak milk yield (r(2)=0.18) nor 305-d milk yield (r(2)=0.29) was accurate for predicting total milk yield per lactation. Year, parity, and season effects had significant influence on milk yield of cows induced into lactation and treated with rbST throughout lactation, and peak milk yield can assist in the prediction of 305-d milk yield but not total milk yield. This study also showed that hormonal induction of lactation in barren high-yielding cows is a reliable, practical, and affordable technique in countries where rbST treatment and prolonged steroid administration of dairy cows are legally permitted.

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Twenty Dorper × Pelibuey primiparous ewes were used to evaluate effects of seasonal ambient heat stress (i.e., spring vs. summer) on physiological and metabolic responses under production conditions in an arid region. Ten ewes experiencing summer heat stress (i.e., temperature = 34.8 ± 4.6 °C; THI = 81.6 ± 3.2 units) and 10 under spring thermoneutral conditions (temperature = 24.2 ± 5.4 °C; THI = 68.0 ± 4.8 units) were corralled together to measure rectal temperature, respiratory frequency, and skin temperatures at 0600, 1200, 1800, and 2400 h on four occasions over 40 days. Blood metabolite and electrolyte concentrations were also measured at 0600 and 1800 hours. Data were analyzed with a completely randomized design using repeated measurements in time. Rectal and skin temperatures, as well as respiratory frequency, were higher (P < 0.01) in summer than spring at all measured days. Blood serum glucose, cholesterol, triglycerides, and chlorine concentrations were lower (P < 0.01) in summer than spring at 0800 and 1800 hours. In contrast, summer heat stress increased (P < 0.01) blood urea and potassium concentrations at 0800 and 1800 hours. Compared with spring thermoneutral conditions, summer heat stress affected the physiological and metabolic status of hair breed ewes in an arid region, which included blood metabolite and electrolyte adjustments to efficiently cope with summer heat stress.

Field studies characterising the forage resources of mixed-breed goats on Chihuahuan Desert rangelands were reviewed and the principal sources of variation in their diet choices discussed. Goats eat a varied diet comprising at least 126 plant species in this landscape. Goats are highly selective feeders, changing their diet from predominantly forbs (8–64%) to browse (35–88%). Graminoids make up only ~5% of the diet, but grasses could be important dietary components on rangelands in good condition. Feed intakes range between 0.8% and 3.4% of bodyweight, depending on the season. DM digestibility of forage selected by goats ranges between 44% and 65%. Annual crude protein (CP) in forages selected by goats varies from 80 to 160 g CP kg–1 DM. Overall, pregnant and lactating goats manage to ingest food that contains higher amounts of CP and lower amounts of cell wall than non-pregnant, non-lactating goats. Goats not adapted to severe shortage of forage select a diet that does not match their nutritional requirements and fetal losses occur. Goat kids select higher quality diets than do mature goats (94.5 vs 88.5 g CP kg–1 DM). Granadina goats eat ~20% more shrubs, including 3-fold more Larrea tridentata (DC) Cav., than Nubian goats. Goats with severely eroded incisors avoid grasses, focusing on tender-leaved shrubs. During the rainy season, bucks select mainly shrubs (78% of the diet) and avoid grasses (1.7% of the diet), whereas does rely heavily on forbs (about one-third of their diet). Alternating use of grazing grounds increases shrub ingestion by 25%. No evidence exists indicating that food choice by goats in this arid environment is biased towards forages with lower secondary compounds. It is concluded that the flexible, broad-scale and opportunistic feeding behaviour of goats make them an effective animal to sustainably exploit the forage resources of the Chihuahuan Desert.

Knowledge on the ecological effects of goat grazing on arid rangeland is far from complete, and specifically there is little scientific information on effects of heavy goat grazing on arid ecosystems. One objective of this study was to determine botanical composition of dairy-type goat diets on heavily (1.5 ha per goat) and lightly (15 ha per goat) grazed Chihuahuan desert