Varying the time since the last meal (i.e. fasting) is a means of manipulating foraging behaviour. Management practices that restrict grazing time, and/or change the timing of the grazing session, may be analogous to changes introduced with different fasting regimes, suggesting that the same pattern of responses on foraging behaviour could be expected. Concepts related to eating patterns of grazing dairy cows are briefly reviewed, and impacts of short-term (i.e. within day) fasts on ingestive behaviours are discussed. Finally, several experiments that examined impacts of short-term fasts on eating patterns, ingestive behaviours and performance of lactating dairy cows are reviewed. Management practices that create shorter grazing sessions (i.e. longer fasting periods before grazing), and/or involve afternoon grazing, result in longer initial grazing bouts, higher intake rates, reductions in rumination time during the grazing session, as well as more pronounced changes in rumen pH, concentrations of rumen fermentation metabolites and rumen load. All of these changes have been associated with improvements in performance of grazing dairy cattle. These concepts and findings have implications in defining optimal grazing strategies, as well as allowing cattle performance, sward conditions and nutrient balances to be predicted and analysed in an integrated manner.

No abstract

Research conducted over recent decades to improve understanding of the functional responses among sward characteristics, intake rate and grazing behaviour has been reviewed. The opportunities to modify grazing pattern by changes in feeding management are discussed and the implications for dairy-farm feeding strategies are highlighted. Progress in the understanding of the functional responses between sward characteristics and intake rate and their main components (bite mass, bite area, bite depth and bite rates) has been substantial. However, progress in understanding the factors that mediate the initiation and the end of individual meals has been poorer and requires further study. Much of the research has been conducted using short-term experiments with a limited number of experimental animals and mostly conducted on mono-specific uniform swards. The physiological state of the animal as well as the maintenance energy associated with grazing strategies have received very little, if any, attention. More integrated (sward, animal, management) and long-term basic research is required to improve feeding practices at the farm level and the design of farms for the new generation of grassland-based dairy-production systems.

Extensive livestock production in southern South America occupies ~0.5 M km2 in central-eastern Argentina, Uruguay and southern Brazil. These systems have been sustained for more than 300 years by year-long grazing of the highly biodiverse native Campos ecosystems that provides many valuable additional ecosystem services. However, their low productivity (~70 kg liveweight/ha per year), at least relative to values recorded in experiments and by best farmers, has been driving continued land use conversion towards agriculture and forestry. Therefore, there is a pressing need for usable, cost effective technological options based on scientific knowledge that increase profitability while supporting the conservation of native grasslands. In the early 2000s, existing knowledge was synthesized in a path of six sequential steps of increasing intensification. Even though higher productivity underlined that path, it was recognized that trade-offs would occur, with increases in productivity being concomitant to reductions in diversity, resilience to droughts, and a higher exposure to financial risks. Here, we put forward a proposal to shift the current paradigm away from a linear sequence and toward a flexible dashboard of intensification options to be implemented in defined modules within a farm whose aims are (i) to maintain native grasslands as the main feed source, and (ii) ameliorate its two major productive drawbacks: marked seasonality and relatively rapid loss of low nutritive value-hence the title “native grasslands at the core.” At its center, the proposal highlights a key role for optimal grazing management of native grasslands to increase productivity and resilience while maintaining low system wide costs and financial risk, but acknowledges that achieving the required spatio-temporal control of grazing intensity requires using (a portfolio of) complementary, synergistic intensification options. We sum up experimental evidence and case studies supporting the hypothesis that integrating intensification options increases both profitability and environmental sustainability of livestock production in Campos ecosystems.

Sixty-four spring-calved primiparous crossbred cows paired by calving date and body condition score (BCS) at calving were used to study the effect of a short-term increase in the nutritional plane before the mating period on cow and calf performance, changes in metabolic and endocrine parameters and hepatic gene expression. At 48 ± 10 days post-partum (onset of nutritional treatment = day 0), cows were assigned to two treatments during 23 days: control (grazing of native pastures; NP; n = 31) and increased nutritional plane (NP improved with Lotus subbiflorous cv Rincon; IP; n = 33). Cow body weight (BW), BCS and total protein and albumin concentrations increased while urea and non-esterified fatty acids levels decreased from the beginning of the nutritional treatment in both groups, indicating the animal positive energy balance as forage growth and availability of pastures increased during spring. In addition, cow BW and BCS, as well as calf average daily gain and BW, were greater in IP than in NP cows groups. Insulin concentrations were less in IP than in NP (1.37 vs. 2.25 ± 0.26 μU/ml) because insulin increased owing to nutritional treatment only in NP cows. Hepatic insulin receptor mRNA at day 23 tended to be 1.5-fold greater, while insulin growth factor binding protein-3 mRNA expression was 1.7-fold greater in NP than in IP cows. Reproductive responses were not affected by nutritional treatment, but days to initiation of ovarian ciclicity (108 ± 10 days) were positively correlated with insulin concentrations. Grazing of improved NP for 23 days before the mating period did not improve cow reproductive performance but modified metabolic, endocrine and gene expression parameters, in agreement with greater nutrient and energy partitioning towards milk production, reflected in better calf performance.

The effects of two levels of herbage allowance (HA, kg DM/kg liveweight (LW)) on forage mass and chemical composition, cow body condition score, cow LW, stocking rate, productive and reproductive responses were evaluated during two consecutive years. Eighty primiparous spring-calving beef cows were allocated to a completely randomised block design of two HA that had an annual average of 2.5 (low) and 4.0 kg DM/kg LW (high) from –150 to 195 days postpartum. The grazing system was continuous, and the put-and-take method was employed to adjust HA. At 86 ± 12 days postpartum, all cows were submitted to calf suckling restrictions with nose plates (12 days) and dietary flushing (2 kg/cow.day of whole-rice bran for 22 days), 6 days before bull introduction. Forage mass was affected by HA (P = 0.004) and year (P = 0.014); the high HA had a greater forage mass than the low HA (1474 vs 1212 ± 86 kg DM/ha; P < 0.05), and Year 2 had a greater forage mass than Year 1 (1545 vs 1134 ± 78 kg DM/ha; P < 0.05). Stocking rate was affected by HA and season (P = 0.0004) interaction. The stocking rate during autumn and spring was greater in low than high HA, and no differences were identified in winter and summer. The body condition score was improved in high HA during autumn and resulted in a greater winter (mid-gestation) body condition score than the low HA without differences during spring-summer (postpartum). Cow LW was lower during autumn, winter and early postpartum (16 days postpartum) in low HA in Year 1 than high HA of Year 1 and high and low HA cows in Year 2. Furthermore, the probability of total pregnancies (0.88 vs 0.59 ± 0.07; P = 0.01) and the calf weight adjusted to 205 days (194 vs 175 ± 16 kg; P < 0.05) were greater in high HA. Calf weight adjusted to 205 days (Year 1: 192 vs Year 2: 177 ± 16 kg; P < 0.05) and survival curves of postpartum anoestrus (P = 0.01) were affected by year but did not affect the probability of conception, early or total pregnancies. In conclusion, the reproductive and productive responses of primiparous beef cows grazing Campos grasslands were improved in high HA and could contribute to alleviating adverse climatic conditions effects.

No abstract

The objectives of the present experiment were to analyse the reproductive and productive responses to suckling-restriction treatments and flushing in primiparous grazing beef cows. During 3 years, 153 primiparous anoestrus cows were assigned randomly to one of four treatments in a 2 by 2 factorial arrangement of suckling-management treatments and flushing. Suckling-restriction treatments started at 61 ± 10 days postpartum and consisted of applying nose plates to calves for 12 days (i.e. TS treatment) or 5 days of isolation of the calf from the cow followed by applying nose plates to calves for 7 days as calves were reunited with their mothers (i.e. IS treatment). Nutritional treatments (flushing v. control) started at the beginning of the breeding season, immediately after the suckling-restriction treatments were finished (73 ± 10 days postpartum), with cows receiving or not receiving 2 kg/day of whole-rice middling for 22 days. Cow body condition score (BCS) was recorded every 20 days from calving until 120 days postpartum. Duration of postpartum anoestrus (PPA) and probability of cyclicity were estimated by plasma progesterone concentrations analysed in weekly samples. Pregnant cows were determined by ultrasound 42 days after bull introduction (early pregnancy; EP) and 30 days after the end of the breeding season (total pregnancy; TP). BCS at calving and changes in BCS from calving to the day of BCS nadir (ΔBCS) varied among years depending on forage availability and weather conditions. Increased cow BCS at calving decreased PPA (b = –41 days, P < 0.0001) and, in interaction with ΔBCS, increased EP (P < 0.008) and TP (P < 0.003). Calf weights at weaning and average daily gain were not affected by suckling-restriction or flushing treatments. Isolated temporary suckling control reduced PPA by 11 days when compared with temporary suckling control (P < 0.004). Flushing increased EP by 40%, which was also affected by BCS at calving and was greater in cows that gained, than in those that maintained or lost BCS. We conclude that flushing was useful in improving early pregnancy rates of primiparous beef cows with ‘suboptimal’ body condition (lower than 4.5) at calving and grazing native pasture.