High genetic merit dairy heifers grazing low quality forage had similar weight gain and urinary nitrogen excretion to those of low genetic merit heifers

Climate variability and increasing drought events have become significant concerns in recent years. However, there is limited published research on body weight (BW) change of dairy heifers with different genetic merit when grazing on drought impacted pastures in southern Australia. Achieving target body weight (BW) is vital for dairy heifers, especially during critical stages like mating and calving. This study aimed to assess dry matter (DM) intake, BW change, urinary nitrogen excretion, and grazing behaviours of high vs. low genetic dairy heifers grazing pasture during a 43-day experimental period in a drought season. Forty-eight Holstein Friesian heifers grazed on ryegrass-dominant pasture and were divided into two groups based on their high and low Balanced Performance Index (HBPI and LBPI, respectively). Each group was further stratified into six plots, with similar BW, resulting in four heifers per replication group. Data from the five measurement days were averaged for individual cows to analyse the dry matter intake, nitrogen intake and nitrogen excretion. The statistical model included the treatment effect of BPI (H and L) and means were analysed using ANOVA. The pasture quality was poor, with metabolizable energy 9.3 MJ/Kg DM and crude protein 5.9% on a DM basis. Nitrogen intake and urinary nitrogen excretion were significantly higher (p  <  0.05) in HBPI compared to the LBPI. However, despite these differences, the study did not find any advantages of having HBPI heifer grazing on low quality forage in terms of BW performance.

Body Condition Score, Rumination, Intake, Milk Production and Milk Composition of Grazing Dairy Cows Supplemented with Rumen-Protected Lysine and Methionine

The study utilised a pasture grazing based, voluntary traffic automatic milking system to investigate milk production of cows fed a pasture-based diet and supplemented with a pellet formulated with vs. without rumen-protected lysine and methionine (RPLM). The study adopted a switch-over design (over two periods of 5 and 10 weeks, respectively) and used 36 cows and equally allocated them into two experimental groups. The RPLM (Trial) pellet had 2% lower crude protein, but similar metabolizable energy content compared to the Control pellet. Pellet intake was 10.0 and 9.4 kg/day/cow. Milk yield was 36.2 and 34.4 kg/day/cow (p = 0.23), and energy corrected milk was 35.1 and 33.8 kg/day/cow (p = 0.076), and milk solids was 2.55 and 2.46 kg/cow/day (p = 0.073) in the Control and Trial groups, respectively. Milk fat%, milk protein%, milk fat: protein ratio, milking frequency and rumination time were not different between the two groups (p > 0.05). In period 1, plasma glucose was 3.1 mmol/L for both groups and milk urea were 150 and 127 mg/L in the Control and Trial groups, respectively. Both plasma glucose (as a proxy for energy supply) and milk urea (as a proxy for nitrogen use efficiency; NUE) were not different between groups (p > 0.05). This study showed that under a grazing pasture system, feeding lactating dairy cows a low protein pellet with RPLM supplementation, maintained milk production performance and NUE, compared with cows fed a high protein Control pellet diet with no RPLM. Further research should assess the long-term (seasonal) effects of feeding a diet formulated with RPLM on cow intake, health and reproductive performance.

Dual-purpose crops: the potential to increase cattle liveweight gains in winter across southern Australia

Context Dual-purpose wheat (Triticum aestivum L.) and canola (Brassica napus L.) crops have been extensively researched for grazing in Australian farming systems, with a focus on grazing by sheep. In some regions, dual-purpose crops have been grazed by cattle, but there have been reports of animal health problems. Aims This paper sought to collate all known experiments conducted throughout Australia of cattle grazing dual-purpose crops, in order to evaluate grazing management options for cattle on dual-purpose crops that result in high growth rates and good animal health outcomes. Methods There were six experiments. In Expts 1–3, cattle were grazed on wheat crops with and without available mineral supplementation of NaCl and MgO in a 1:1 ratio. In Expt 3, lime was also added to the mineral mix. In Expts 4 and 5, dual-purpose crops were grazed in combination with annual pastures to determine whether strategic use of dual-purpose crops could increase whole farm livestock productivity. In Expt 6, cattle were introduced to dual-purpose canola with different periods of adaptation (0, 4 and 7 days). Liveweight gain was monitored regularly to assess differences between adaptation treatments. Key results Liveweight gain was increased by 0–27% when cattle grazing high quality, dual-purpose wheat were provided with mineral supplement. Cattle had an initial lag in growth rate when introduced to dual-purpose canola for grazing and this was not affected by the adaptation strategy used. Cattle that experienced a shorter adaptation period achieved higher weight gains more quickly. After the lag phase, average daily gain (ADG) was ≥2 kg/head.day, with an ADG over the entire grazing period for all treatments of 1.75 kg/head.day. The effect on the farm system was determined by extending the length of the grazing period on the dual-purpose crops. Grazing periods of shorter duration did not increase overall liveweight gains compared with grazing only pasture, whereas extending the period of dual-purpose crop grazing resulted in increased cattle weights. Conclusions Cattle benefit from the addition of mineral supplements when grazing a dual-purpose wheat crop, with a response similar to that previously demonstrated in sheep. Cattle can safely graze dual-purpose canola and achieve high ADG. Inclusion of dual-purpose crops can improve overall cattle performance in the farming system. Implications The potential area for production of dual-purpose crops within the Australian mixed farming zone is large and there may be insufficient livestock numbers within the zone to utilise the potential forage production. Cattle from other regions could be introduced during autumn and winter to realise this large forage potential during a period that is commonly a feed deficit on grazing-only properties. Estimates suggest that up to two million young cattle could be supported for 60 days, increasing liveweight by 90 kg/head.

Climate Change Impact, Adaptation, and Mitigation in Temperate Grazing Systems: A Review

Managed temperate grasslands occupy 25% of the world, which is 70% of global agricultural land. These lands are an important source of food for the global population. This review paper examines the impacts of climate change on managed temperate grasslands and grassland-based livestock and effectiveness of adaptation and mitigation options and their interactions. The paper clarifies that moderately elevated atmospheric CO2 (eCO2) enhances photosynthesis, however it may be restiricted by variations in rainfall and temperature, shifts in plant’s growing seasons, and nutrient availability. Different responses of plant functional types and their photosynthetic pathways to the combined effects of climatic change may result in compositional changes in plant communities, while more research is required to clarify the specific responses. We have also considered how other interacting factors, such as a progressive nitrogen limitation (PNL) of soils under eCO2, may affect interactions of the animal and the environment and the associated production. In addition to observed and modelled declines in grasslands productivity, changes in forage quality are expected. The health and productivity of grassland-based livestock are expected to decline through direct and indirect effects from climate change. Livestock enterprises are also significant cause of increased global greenhouse gas (GHG) emissions (about 14.5%), so climate risk-management is partly to develop and apply effective mitigation measures. Overall, our finding indicates complex impact that will vary by region, with more negative than positive impacts. This means that both wins and losses for grassland managers can be expected in different circumstances, thus the analysis of climate change impact required with potential adaptations and mitigation strategies to be developed at local and regional levels.