Pasture dry matter intake per cow in intensive dairy production systems: effects of grazing and feeding management.

The competitiveness and sustainability of low input cost dairy production systems are generally supported by efficient use of pasture in the diets. Therefore, pasture intake directly affects overall efficiency of these systems. We aimed to assess feeding and grazing management main factors that affect pasture dry matter intake (DMI) in commercial dairy farms during the different seasons of the year. Fortnightly visits to 28 commercial dairies were carried out between June 2016 and May 2017 to record production and price, supplement offered and price, pasture access time (PAT), herbage mass (HM) and allowance (HA). Only farms with the most contrasting estimated pasture DMI per cow (eDMI) were compared as systems with high (HPI; N = 8) or low (LPI; N = 8) pasture DMI. Despite a lower individual milk production in HPI than LPI (19.0 v. 23.3 ± 0.7 l/cow, P < 0.01), daily margin over feeding cost was not different between groups (3.07 v. 2.93 ± 0.15 U$S/cow for HPI and LPI, respectively). During autumn and winter, HPI cows ingested more pasture than LPI cows (8.3 v. 4.6 and 5.9 v. 2.9 ± 0.55 kg DM/cow per day, respectively, P < 0.01) although PAT, HM and HA were similar between groups. Both groups offered high supplementation levels during these seasons, even though greater in LPI than HPI (14.7 v. 9.7 ± 0.7 kg DM supplement/cow per day, respectively, P < 0.01). On the other hand, differences between groups for both pasture and supplement DMI were more contrasting during spring and summer (13.1 v. 7.3 ± 0.5 and 4.0 v. 11.4 ± 0.4 kg DM/cow per day for HPI and LPI, respectively, P < 0.01), with higher PAT in both seasons (P < 0.05) and higher HA during summer in HPI than LPI (P < 0.01). Unlike LPI, during these seasons HPI adjusted offered supplement according to HA, achieving a higher pasture eDMI and making more efficient use of available pastoral resource than LPI. As there was no grazing limiting condition for pasture harvesting in either group, the main factor affecting pasture DMI was a pasture by supplement substitution effect. These results reinforce the importance of an efficient grazing management, and using supplements to nutritionally complement pasture intake rather than as a direct way to increase milk production.

Effect of timing of corn silage supplementation to Holstein dairy cows given limited daily access to pasture: intake and performance.

The timing in which supplements are provided in grazing systems can affect dry matter (DM) intake and productive performance. The objective of this study was to evaluate the effect of timing of corn silage supplementation on ingestive behaviour, DM intake, milk yield and composition in grazing dairy cows. In total, 33 Holstein dairy cows in a randomized block design grazed on a second-year mixed grass-legume pasture from 0900 to 1500 h and received 2.7 kg of a commercial supplement at each milking. Paddock sizes were adjusted to provide a daily herbage allowance of 15 kg DM/cow determined at ground level. The three treatments imposed each provided 3.8 kg DM/day of corn silage offered in a single meal at 0800 h (Treatment AM), equally distributed in two meals 0800 and 1700 h (Treatment AM-PM) or a single meal at 1700 h (Treatment PM). The experiment was carried out during the late autumn and early winter period, with 1 week of adaptation and 6 weeks of measurements. There were no differences between treatments in milk yield, but 4% fat-corrected milk yield tended to be greater in AM-PM than in AM cows, which did not differ from PM (23.7, 25.3 and 24.6±0.84 kg/day for AM, AM-PM and PM, respectively). Fat percentage and yield were greater for AM-PM than for AM cows and intermediate for PM cows (3.89 v. 3.66±0.072% and 1.00 v. 0.92±0.035 kg/day, respectively). Offering corn silage in two meals had an effect on herbage DM intake which was greater for AM-PM than AM cows and was intermediate in PM cows (8.5, 11.0 and 10.3±0.68 kg/day for AM, AM-PM and PM, respectively). During the 6-h period at pasture, the overall proportion of observations on which cows were grazing tended to be different between treatments and a clear grazing pattern along the grazing session (1-h observation period) was identified. During the time at pasture, the proportion of observations during which cows ruminated was positively correlated with the DM intake of corn silage immediately before turn out to pasture. The treatment effects on herbage DM intake did not sufficiently explain differences in productive performance. This suggests that the timing of the corn silage supplementation affected rumen kinetics and likewise the appearance of hunger and satiety signals as indicated by observed changes in temporal patterns of grazing and ruminating activities.

Milk fatty acid profile from cows fed with mixed rations and different access time to pastureland during early lactation.

Milk fatty acid (FA) profiles were determined in Holstein cows (n = 27) fed total mixed rations (TMR) ad libitum (G0) or diet composed by TMR (50% dry matter [DM] offered) plus grazing of pasture with 6 hr of access time to paddock in one session (G1) or 9 hr in two sessions (G2) at 45 days in milk (DIM). Moreover, milk FA was determined at 65 DIM when G0 cows turned out to G1 diet without adaptation period (Post-G0), G1 remained as controls. Milk FA was quantified using gas chromatography and mass spectrometry. Preformed FA at 45 DIM was greater (+27%) for G2 than G0 cows (p < .05). Stearic acid (C18:0) was 30% greater for G2 cows (p < .05). De novo FA was lowest for G2 cows (p < .05). Conjugated linoleic acid (CLA) did not differ (p < .12), while vaccenic acid (C18:1trans) was twofold greater for grazing treatments (p < .01). Linolenic acid [C18:3(n-3)] was greatest for G2 and lowest for G0 cows (p < .01). Omega 6 FA was greater for G0 than grazing cows, mainly due to linoleic acid [18:2cis(n-6); p < .05]. These results determined that n-6/n-3 ratio was almost threefold greater for G0 than grazing cows (p < .001). When diet of G0 cows changed to include pasture (Post-G0), preformed FA increased (p < .05), explained mainly by the increase (p < .05) of stearic (C18:0) and C18:1trans, while de novo FA tended to decrease (p < .1). Moreover, the amount of CLA and C18:3(n-3) tended to increase (p < .1) in Post-G0 cows. Offering 50% of dietary DM from pasture modified milk FA profile in early lactation potentially beneficial for human health. When TMR-fed cows were turned out to 50% pasture, milk FA profile reflected dietary change without need of an adaptation period.

Endometrial gene expression in primiparous dairy cows at the end of the voluntary waiting period is affected by nutrition: Total mixed ration vs increasing levels of herbage allowance.

The study postulated that differential nutritional management during the early lactation period would be reflected in endometrial expression of genes related to embryo growth at the end of the voluntary waiting period. Thus, the effect of the combined use of total mixed ration (TMR) and grazing under different herbage allowances during the first 75 days post-partum (DPP) on endometrial gene expression was evaluated in primiparous dairy cows. Cows were blocked by body weight, age and body condition score and randomly assigned to three grazing treatments: high (HA, 30 kg DM per cow per day), medium (MA, 15 kg DM per cow per day) and low (LA, 7.5 kg DM per cow per day) herbage allowance (mixed pasture, 2,600 kg DM per ha) plus 8 kg DM of supplement or TMR (55% forage, 45% concentrate) fed ad libitum (TMR) from calving to 75 DPP. At 57 DPP, cows were synchronized for oestrus (day 0, 68 DPP) and at day 7, endometrial biopsies were obtained. The nutritional treatment did not affect insulin, IGF-1 and leptin concentrations on days 0, 4 or 7. Expression of IGF1, IGFBP3, IGFBP4, ADIPOR1 and ADIPOR2 mRNA was significantly affected by the nutritional treatment. Endometrial IGF1 and IGFBP4 mRNA were twofold greater in TMR and HA than MA and LA cows. Expression of IGFBP3 and ADIPOR1 mRNAs was greater in TMR and HA than MA cows, but did not differ from LA cows. All groups had greater expression of ADIPOR2 mRNA than MA cows. This study provided solid evidence of the importance of nutritional management during early lactation on uterine environment at the end of the voluntary waiting period. The greater expression of genes related to embryo growth and uterine function (IGF system, progesterone and adiponectin receptors) in cows fed diets maximizing energy intake suggests a favourable environment for embryonic growth, which may explain the improved reproductive performance of cows in good energy balance.

Association of SNP of neuropeptide Y, leptin, and IGF-1 genes with residual feed intake in confinement and under grazing condition in Angus cattle.

In this study we quantify and compare the phenotypic variation in residual feed intake (RFI) in 2 groups of Angus female calves: one carrying simultaneously putative favorable allelic variants (SNP) of neuropeptide Y, leptin, and IGF-1 genes (VAL group) and another devoid of such alleles (CON group). We performed 2 sequential trials: under confinement feeding a high-concentrate diet and under grazing condition. In confinement, 38 purebred Angus female calves [mean age and BW of 247 d (SD = 15) and 186 kg (SD = 33.2), respectively] were offered a total mixed ration diet (60:40 concentrate: alfalfa hay, as fed) ad libitum during 57 d. Dry matter intake was estimated from the difference between offered and refused feed; BW was recorded every 2 wk. Under grazing, 12 heifers from each group were ranked by BW and RFI and randomly assigned to 4 pasture paddocks. Heifers were continuously stocked at high-quality, high-herbage-mass mixed pasture. Herbage DMI was determined using the n-alkane technique. Different models were used to determine RFI: models that use phenotypic data [RFI as described by Koch et al. (1963; RFIK) and RFI as described by ME (RFIME)] and models that use standards feeding data [RFI estimated by Fan et al. (1995; RFIF) and RFI in which the expected DMI was derived from equations in Standing Committee on Agriculture (1990; RFISCA)]. Least squares mean values (SE) of DMI (kg/d), metabolizable energy intake (MEI; Mcal/d), ADG (kg), RFIK (kg DM/d), and feed conversion ratio (FCR; kg DMI/kg ADG) for VAL and CON genotype groups were 6.65 and 6.89 (0.49), 16.7 and 17.4 (1.44), 1.24 and 1.24 (0.03), -0.11 and 0.11 (0.09), and 5.8 and 5.8 (0.14), respectively, in the confinement trial. In the grazing trial least squares mean values (SE) of herbage DMI (kg/d), ADG (kg), MEI (Mcal/d), RFIK, and FCR of VAL and CON groups were 8.76 and 10.93 (0.71), 1.4 and 1.37 (0.05), 25.5 and 31.7 (2.09), -1.02 and 1.02 (0.42), and 6.41 and 6.96 (0.46), respectively. Genotyped groups tended to differ in DMI (P = 0.10), in MEI (P = 0.06), and in RFIK (P = 0.10), differed in RFIF (P = 0.010), and did not differ in ADG or FCR during confinement. During grazing, genotyped groups differed in DMI (P = 0.005), in MEI (P = 0.006), and in RFIK (P = 0.002) but did not differ in ADG and FCR. Our results demonstrate a strong association between these 3 SNP and RFI when animals were grazing on a high-quality, high-availability pasture, whereas a weak effect was observed under confinement.

Challenges in the nutrition and management of herbivores in the temperate zone.

The expected higher global demand for animal proteins and the competition for starch and sugars between food, fuel and feed seem to favour herbivores that convert solar energy captured in fibrous plants into animal products. However, the required higher production level of herbivores questions the sustainability of this conversion. An increase in herbivore production can be achieved by increasing the number of animals associated with the increasing demand of plant biomass or by improving the efficiency with which plant biomass is converted into meat and milk. The potential to increase food production by cattle, the main food-producing herbivore in the temperate zones outside China, was considered in three production systems: grassland-based, mixed rain-fed and mixed irrigated systems. The potential to increase plant biomass production in grassland-based systems seems limited, unless fertiliser is imported in large quantities and crop production is increased, sacrificing valuable, high-quality grasslands, which often conflicts with sustainable production methods. Also, in mixed systems with high inputs of fertiliser or water, improvements in plant biomass production seem marginal and the main challenges for these systems are in breeding high-quality plant biomass at lower levels of fertiliser and the use of new co-products from food processing and bio-based economies. Consequently, the main challenge in herbivore nutrition management is to improve the efficiency of plant biomass utilisation. Stocking rate management along with seasonal variation in the grazing capacity of grasslands and moderate use of fertiliser may increase meat production in grassland-based systems by 400%. Improving plant biomass utilisation in the more industrialised mixed rain-fed systems seems possible by better feed storage technologies and for dairy cattle by improving animal health and lifetime production level. Managing the transition period seems crucial to achieve more sustainable mixed rain-fed and mixed irrigated dairy production systems. Whether sustainable production methods will be implemented also depends on macro-economic conditions and awareness of regional and global environmental concerns.

Studies of the transition cow under a pasture-based milk production system: metabolic profiles.

This study describes the effect of parity (multiparous versus primiparous) and body condition score (BCS) at calving (<3 or > or =3; scale 1-5) on variations of BCS, body weight (BW) and metabolic profiles in Holstein cows grazing on improved pastures. Forty-two cows were studied (21 multiparous and 21 primiparous) from 2 months before to 3 months after calving. BCS, BW and milk production were measured every 2 weeks. Blood samples were taken every 2 weeks to determine total protein, albumin, urea, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), cholesterol, aspartate aminotransferase (AST), calcium, phosphorus and magnesium. Primiparous cows had lower BCS during the early postpartum (PP) period and produced less milk than multiparous. In primiparous cows NEFA concentrations were higher during the early postpartum period; BHB levels were similar in both categories during this period. Primiparous cows showed a more unbalanced metabolic profile than multiparous cows, reflecting that they are recovering from the loss of BCS after calving with less success.

Effects of parity and body condition at parturition on endocrine and reproductive parameters of the cow.

The effect of parity (multiparous vs primiparous) and body condition score (BCS; <3.0 or > or =3.0, lean vs fat) at parturition on metabolic and endocrine profiles from 1 month before to 2 months after parturition were studied in 42 Holstein cows grazing on improved pastures. BCS and milk production were determined every 2 weeks. Non-esterified fatty acids (NEFA), beta-hydroxy-butyrate (BHB), insulin, IGF-I, leptin, thyroxine (T4) and 3,3',5-tri-iodothyroinine (T3) were determined in plasma every 10 days. Progesterone was determined three times per week after parturition. Primiparous cows had a lower BCS during the early postpartum period and produced less milk than multiparous animals. Primiparous cows had higher NEFA concentrations and they presented more samples with BHB concentrations of >1 mmol/l than multiparous cows. Multiparous cows had higher T3, T4 and IGF-I concentrations, while fat cows had higher leptin and IGF-I concentrations. All hormone concentrations were diminished in the first week postpartum. Primiparous cows and fat cows presented a steeper decay of IGF-I and leptin around parturition than multiparous cows and lean cows. While thyroid hormones and IGF-I showed increasing concentrations from approximately day 30, leptin concentrations remained low until the end of the experimental period. The initiation of ovarian cyclicity was delayed in primiparous cows and especially in primiparous lean cows, consistent with longer intervals from parturition to first service and to conception. The endocrine signals most likely to inform the reproductive axis regarding a negative energy balance were IGF-I and leptin.

Duration of regrowth of ryegrass (Lolium perenne) effects on grazing behavior, intake, rumen fill, and fermentation of lactating dairy cows.

The relative importance of duration of sward regrowth and fill and fermentation in the rumen on the control of grazing time and intake rate during the first grazing session of the day was studied. Four lactating dairy cows were allowed to graze ryegrass (Lolium perenne) swards, with five different regrowth periods after mowing (6, 9, 16, 22, and 30 d). The cows were allowed to graze until they stopped voluntarily (cessation of grazing activity for at least 15 min). Before and after grazing the rumen contents were evacuated, weighed, sampled, and returned to the animals. Samples of rumen liquid were taken immediately before rumen evacuation and approximately 30, 60, 120, and 240 min after the grazing session was finished. Grazing time and intake rate did not follow a significant trend with period of regrowth. Bite rate did not change significantly with duration of regrowth with cows exhibiting high rates of biting for all the sward conditions. Rumen pools sizes of dry matter, neutral detergent fiber, and volatile fatty acids (VFA), measured after grazing, increased significantly with days of sward regrowth, even though the changes over days were small. Concentration of VFA followed a significant quadratic trend with a maximum concentration observed at approximately 110 min after cessation of grazing. In this study, rumen fill, VFA (either total or major components), ammonia, pH, and osmotic pressure as individual variables were not correlated with grazing time or dry matter intake.