No abstract

This study investigated the energy balance, metabolic changes, reproduction, and health in Australian Holstein-Friesian cows of average genetic merit fed to produce 6,000 L of milk/cow per lactation (restricted production; Rp) on a predominantly grazed pasture diet, or 9,000 L of milk/cow per lactation (high production: Hp) on a more intensive feeding regimen by using a partial mixed ration to supplement pasture. The mean 4% fat-corrected milk (FCM) and standard deviation achieved was 8,466 +/- 1,162 L/cow per lactation for the Hp herd and 6,748 +/- 787 L/cow per lactation for the Rp herd. During early lactation, the degree of estimated negative energy balance was less in the Hp cows than in the Rp cows (-16.1 vs. -29.1 MJ/cow per day, respectively). Consequently, the mobilization of body reserves was also lower in the Hp cows, and this was reflected in lower concentrations of nonesterified fatty acids (0.70 vs. 0.84 mmol/L) and beta-hydroxybutyrate (0.51 vs. 0.69 mmol/L) and greater concentrations of glucose (3.51 vs. 3.34 mmol/L) and insulin-like growth factor-I (78.9 vs. 58.7 ng/mL) for Hp and Rp cows, respectively. After calving, body condition score and body weight decreased to a similar extent in both herds and did not reflect the differences in mobilization of body reserves between the 2 herds. Reproductive performance was not significantly related to level of milk yield. The mean interval from calving to first active corpus luteum was 33 (SD = 20) d postpartum, and there were 1.4 (SD = 0.8) estrus cycles before the beginning of the breeding period (>50 d postpartum). The interval from calving to pregnancy was 114 d, and the pregnancy rate after 12 wk of mating was 74%. The number of cows with ovarian abnormalities was also similar between the 2 herds. Cows with a long postpartum anestrus had the lowest concentration of insulin-like growth factor-I. The number of health-related disorders was also similar between the herds, with the exception of mastitis, for which the incidence was significantly greater in the Hp cows. The results indicate that the production per cow could be increased from 6,748 L of FCM/cow per lactation for cows grazing pasture and supplemented with concentrates only at milking to 8,466 L of FCM/ cow per lactation, in one lactation, by supplementing pasture with a partial mixed ration. Despite the fact that production per cow increased substantially, the degree of estimated negative energy balance and the metabolic changes in early lactation were lower and reproductive performance was maintained.

A grazing experiment involving 50 lactating Holstein–Friesian dairy cows was conducted to test the hypothesis that feeding concentrates (range 3–7 kg as fed/cow.day; average 5 kg/cow.day) to grazing cows based on individual (I) cow requirements would increase milk solids yield in comparison to fixed rate (F) allocation to the whole herd (average 5 kg/cow.day for all cows). The experiment comprised two sequential periods that differed only in the way maize silage was offered to cows (either 100% on a feed pad at night or 75% on a feed pad at night, with 25% in a paddock in the morning). Intake of individual cows was estimated using the 13C and n-alkanes method. The rumen degradability of the feeds (lucerne pasture, maize silage and commercial dairy pellets) was measured in parallel, using six rumen-fistulated sheep. Compared with cows in the F group, milk yield and milk fat yield for the I cows increased (P < 0.05) by 3.0 and 11.1%, respectively. As neither milk protein content nor milk protein yield was affected (P > 0.05) by treatment, total milk solids yield (milk fat plus milk protein) was 7.0% higher (P < 0.05) for I cows than for F cows. The increase in milk fat yield was presumably associated with an improved diet nutrient balance in the I cows, as indicated by a significant correlation between fibre intake and milk fat yield for cows in the I group but not for cows in the F group. This is also supported by the results of the rumen degradability of the feeds. In this study, higher-producing cows compensated for their higher requirements by increasing intake of maize silage, rather than pasture, as the former was the less restricted feed on offer. This highlights the importance of offering at least one feed to cows in a less restricted way, in order to enable high-producing cows in the herd to compensate for their higher intake requirements. In conclusion, under the conditions of the present study, feeding concentrates to cows based on individual cow requirements increased milk solids yield at no extra cost.

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. The diversity of climate, region, land tenure, herd size and poverty level potentially influence livestock farming. To detect areas of opportunity in the use of human, animal and natural resources, and to determine the degree of technological penetration, a structured questionnaire was administered as personal interviews to 3280 producers. Over 50% of farmers have an activity other than cattle breeding, mostly raising crops and other livestock. Weaned calves, primarily destined for the national market, are the foremost commercial product. Nevertheless, 20% of farmers in the northern region export their calves. European X Zebu crossbred cattle are widespread (over 45% of operations), followed by Bos taurus taurus breeds (22%). Criollo and predominantly Zebu cattle are present in <15% of farms, and dairy breeds in <5%. Over 70% of producers declared to select animal breed based on productive traits and adaptability, even though only 52% have record-keeping systems. The customary method to register data is hand-written, and < 7% of producers use computers. Recorded information comprises data on reproduction (59.1%), calves (44%), herd health practices (32%) and purchases and sales (28%). Over 95% of farmers identify animals by hot iron marks and National Individual Livestock Identification System (SINIIGA) ear tags. Close to 52% of animal breeders do not receive technical advice. Finally, according to producers, the main constraints for farm growth and profitability were lack of access to credit, followed by low market value of their products and insufficient infrastructure.

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. 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 yearround 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