Michael Egan

Although 3-NOP has been proven to reduce enteric methane (CH₄) by ∼30% in indoor systems of dairying when the additive is mixed throughout a total mixed ration (TMR), there has been very limited research to date in grazing systems in which the most convenient method of additive supplementation is at milking twice daily. To investigate the effect of twice daily 3-NOP supplementation on enteric CH₄ emissions, a 12-week study was undertaken in which treatment cows (n = 26) were supplemented with 3-NOP (80 mg per kg dry matter intake; DMI) twice daily at morning and evening milking, while control cows (n = 26) received no additive supplementation. Enteric CH₄, hydrogen (H₂) and carbon dioxide (CO₂) were measured using GreenFeed units, while milk production, body weight (BW), body condition score (BCS) and DMI were monitored to determine the effect of 3-NOP supplementation on productivity. There was no significant effect of 3-NOP supplementation on any of the aforementioned parameters with the exception of CH₄ and H₂ production, respectively. Cows supplemented with 3-NOP produced ∼36% more H₂ (P < 0.001) across a 24-h period, with reductions in CH₄ production of 28.5% recorded in the 3 h after additive consumption (P < 0.001), however, levels of CH₄ production returned to that of the control group thereafter. When CH₄ production was considered across the entire 24-h period, the cows offered 3-NOP produced ∼5% less CH₄ than the control (P < 0.050). Future research should focus on methods to increase the efficacy of the additive throughout the day which would include the deployment of a slow-release form or an out of parlor feeding system that allows animals consume the product at additional time points.

Over the winter period, the low grass growth and availability in pasture-based dairy systems results in animals being housed and predominantly fed a diet of grass silage. There is limited availability of methane (CH₄) data evaluating the impact of forage type on dairy cows over the pre-partum period. The objective of the current experiment was to evaluate the impact of feeding grass clover (GC) silage and grass-only (GO) silage on the dry matter intake (DMI) and enteric CH₄ emissions of dairy cows pre-partum. A complete randomised block design was utilised for the 6-week experiment over two winter periods: from December 2020 to January 2021 and from December 2021 to January 2022. In each year, 30 non-lactating pregnant dairy cows were randomly allocated to two treatments (n = 15). In both years, cows in the GC treatment were offered grass clover bale silage, while cows in the GO treatment were offered grass-only pit silage. The DMI and gaseous emissions of individual animals were monitored daily using Hokofarm RIC (roughage intake control) feed stations and the GreenFeed technology. GC silage consistently had greater (p< 0.05) organic matter (OM) digestibility and lower (p< 0.05) neutral detergent fibre (NDF) and acid detergent fibre (ADF) contents when compared with GO silage. Cows in the GC treatment had significantly greater (p< 0.05) total DMI (TDMI) compared with cows in the GO treatment. The daily CH₄ emissions (in grams per day) were not affected by treatment; however, cows in the GC treatment had reduced (p< 0.05) CH₄ yield (in grams per kilogram TDMI). Offering dairy cows GC silage over the pre-partum period resulted in greater DMI with reduced CH₄ yield when compared with cows offered GO silage.

Early lactation is a critical period for dairy cows, as energy requirements rapidly increase with the onset of lactation; however, early-lactation DMI in pasture-based systems are under measured. The objectives of this study were (1) to measure and profile total DMI (TDMI) and animal performance of dairy cows during early lactation in a pasture-based system, (2) to investigate early-lactation energy balance in pasture-based systems, and (3) to examine production efficiencies, including TDMI and milk solids production per 100 kg of BW. Eighty spring-calving dairy cows were allocated to a grazing group as they calved over a 2-yr period (2021 and 2022). Cows were offered a daily herbage allowance to achieve a postgrazing sward height of 4 cm, with silage supplementation when necessary due to inclement weather. Total DMI was measured using the n-alkane technique over a 12-wk period from February 1, 2021, to April 23, 2022. Total DMI and daily milk yield were significantly affected by parity with both variables being greatest for third-parity animals (17.7 kg of DM and 26.3 kg/cow per day, respectively), lowest for first parity (13.2 kg of DM and 19.6 kg/cow per day, respectively) and intermediate for second-parity animals (16.8 kg of DM and 24.1 kg/cow per day, respectively). Peak TDMI was reached on wk 10 for first-parity animals (14.6 kg of DM), wk 11 for second parity animals (19.3 kg of DM) and wk 12 for third-parity animals (19.9 kg of DM). Parity also had a significant effect on unité fouragère lait (UFL; feed units for milk) feed balance as first-parity animals experienced a greater degree of negative energy balance (-3.2 UFL) compared with second- and third-parity animals (-2.3 UFL). Breed and parity had an effect on production efficiencies during the first 12 wk of lactation as Jersey × Holstein Friesian cows had greater TDMI/100 kg of BW and milk solids/100 kg of BW compared with Holstein Friesian cows.

Similar to all dairy systems internationally, pasture-based dairy systems are under increasing pressure to reduce their greenhouse gas (GHG) emissions. Ireland and New Zealand are 2 countries operating predominantly pasture-based dairy production systems where enteric CH₄ contributes 23% and 36% of total national emissions, respectively. Ireland currently has a national commitment to reduce 51% of total GHG emissions by 2030 and 25% from agriculture by 2030, as well as striving to achieve climate neutrality by 2050. New Zealand's national commitment is to reduce 10% of methane emissions by 2030 and between 24% and 47% reduction in methane emissions by 2050. To achieve these reductions, factors that affect enteric methane (CH₄) production in a pasture-based system need to be investigated. The objective of this study was to assess the relationship between enteric CH₄ and other animal traits (feed intake, metabolic liveweight, energy corrected milk yield, milk urea concentration, and body condition score [BCS]) in a grazing dairy system. Enteric CH₄ emissions were measured on 45 late lactation (213.8 ± 29 d after calving) grazing Holstein-Friesian and Holstein-Friesian × Jersey crossbred cows (lactation number 3.01 ± 1.65, 538.64 ± 59.37 kg live weight, and 3.14 ± 0.26 BCS) using GreenFeed monitoring equipment for 10 wk. There was a training period for the cows to use the GreenFeed of 3 wk before the 10-wk study period. The average enteric CH₄ produced in the study was 352 g ± 45.7 g per day with an animal to animal coefficient of variation of 13%. Dry matter intake averaged 16.6 kg ± 2.23 kg per day, while milk solids (fat plus protein) averaged 1.62 kg ± 0.29 kg per day. A multiple linear regression model indicated that each one unit increase in energy corrected milk yield, metabolic liveweight and milk urea concentration, resulted in an increase in enteric CH₄ production per day by 3.9, 1.74, and 1.38 g, respectively. Although each one unit increase in BCS resulted in a decrease in 39.03 g CH₄ produced per day. When combined, these factors explained 47% of the variation in CH₄ production, indicating that there is a large proportion of variation not included in the model. The repeatability of the CH₄ measurements was 0.66 indicating that cows are relatively consistently exhibiting the same level of CH₄ throughout the study. Therefore, enteric CH₄ production is suitable for phenotyping.

Autumn grazing management aims to accumulate herbage for defoliation prior to a decrease in growth rates for the extension of the grazing season. The current study investigated the impact of building different target herbage masses (THMs) in autumn and imposing one of three different defoliation dates (DDs) between mid-October and late November on light transmitted to the base of the sward, free leaf lamina (FLL), leaf stage and internode elongation. Four THMs (low, medium, high and very high) and three DDs (DD1—15 October, DD2—7 November and DD3—21 November) were assigned to a 4 × 3 split plot design over two years. Light transmitted to the base of the sward was greatest in the low THM and decreased in all other THMs. Internode elongation increased in tillers in the medium to the very high THMs. Defoliation of the medium, high and, in particular, the very high THMs earlier in autumn reduced the effect of decreased light transmission on internode elongation. This study highlights that, as light transmitted to the base of the sward decreases, internode elongation increases, and this could negatively impact sward structure.

The objectives of this study were to investigate the effect of level and timing of silage supplementation during early lactation on animal performance and dry matter intake (DMI). Two farm-lets were established with a high (1253 kg DM/ha) and low (862 kg DM/ha) grass availability at turnout. In spring, cows were assigned to one of two treatments as they calved over 2 years; high grass (HG) and low grass (LG). During period 1 (week 1–6), cows on the HG treatment were offered a high daily herbage allowance (DHA) with low silage and the LG treatment were offered a low DHA with high silage. In period 2 (week 7–12), half of the cows from the HG treatment in P1 switched to the LG treatment in P2 and vice versa as 20 LG cows in P1 switched to the HG treatment in P2. Cows on the HG treatment in P2 received a high DHA with no silage and the LG treatment received a low DHA with 3 kg DM/cow silage. Grass DMI was significantly higher for the HG treatment during both periods (+1.6 and +3.4 kg DM/cow/day, respectively). The HG treatment produced +0.9 kg milk/cow/day and had a higher protein concentration (+1.1 g/kg milk) compared to cows on the LG treatment during period 2. Differences in animal performance observed in period 2 were maintained throughout the 8-week carryover period.

In pasture-based dairy production systems, identifying the appropriate stocking rate (SR; cows/ha) based on the farm grass growth is a key strategic decision for driving the overall farm business. This paper investigates a number of scenarios examining the effects of SR (2–3 cows/ha (0.25 unit changes)), annual nitrogen (N) fertilizer application rates (0–300 kg N/ha (50 kg/ha unit changes)), soil type (heavy and a free-draining soil) and agroclimate location ((south and northeast of Ireland) across 16 years) on pasture growth and forage self-sufficiency using the pasture-based herd dynamic milk model merged with the Moorepark St Gilles grass growth model. The modelled outputs were grass growth, grass dry matter intake, silage harvested and offered, overall farm forage self-sufficiency and N surplus. The model outputs calculated that annual grass yield increased from 9436 kg DM/ha/year when 0 kg N/ha/year was applied to 14 996 kg DM/ha/year when 300 kg N/ha/year were applied, with an average N response of 18.4 kg DM/kg N applied (range of 9.9–27.7 kg DM/kg N applied). Systems stocked at 2.5 cows/ha and applying 250–300 kg N fertilizer/ha/year were self-sufficient for forage. As N input was reduced from 250 kg N/ha/year, farm forage self-sufficiency declined, as did farm N surplus. The results showed that a reduction in N fertilizer application of 50 kg/ha/year will require a reduction in an SR of 0.18 cows/ha to maintain self-sufficiency (R² = 0.90).

Autumn closing date (CD) in intensive pasture‐based systems influences spring herbage availability. Little is known about the impact of earlier closing of swards in autumn on sward structure. A two‐year experiment was undertaken to investigate the impact of five CD on herbage production, leaf extension rate (LER), leaf senescence rates (LSR), sward free leaf lamina (FLL) content and the production and survival of tillers over winter and into spring. The five CD ranges were October 1–15 (CD1), October 16–30 (CD2), October 31––November 14 (CD3), November 15–29 (CD4), November 30–December 14 (CD5) and sward measurements were made on four measurement dates (MD): December 11 (MD1), January 6 (MD2), January 27 (MD3) and prior to spring defoliation (MD4). Thirty perennial ryegrass tillers were measured until the first defoliation in spring (average 1 March). Herbage mass was greatest in early CD and tillers had greater LER and LSR (4.6 and 4.5 mm tiller⁻¹ day⁻¹ respectively) compared to swards with a later CD (3.2 and 2.3 mm tiller⁻¹ day⁻¹ respectively). Early CD had greater parent and daughter tiller mortality than later CD (parent tiller mortality 1.1 and 0.3 ± 0.19 tillers; daughter tiller mortality 1.1 and 0.3 ± 0.27 tillers respectively). Early CD also had greater LER and LSR in daughter tillers (2.6 and 1.5 mm tiller⁻¹ day⁻¹, respectively) compared to late (1.5 and 0.5 mm tiller⁻¹ day⁻¹, respectively). Earlier closing of sward increased herbage mass in spring, however, there were negative implications, such as increased LSR and tiller mortality.