Milk fat is the most variable component of bovine milk and maintaining adequate milk fat percentage continues to be a challenge on grazing dairy farms at key times of the year [ 1]. Although both milk fat percentage and composition are influenced by factors such as genetics, stage of lactation, season and cow health; the diet of the cow has a profound effect on milk fat production [ 2, 3]. The normal milk fat percentage for Holstein herds has been defined as between 3.4% and 4.0% with some seasonal variation [ 4]. The average milk fat percentage of the Irish dairy cow population is 4.22%, where the predominant breed used is Holstein Friesian and where the diet is predominantly pasture based [ 5]. A reduction in milk fat yield in the presence of normal or expected milk yield, or yield of other milk components including milk protein, can be identified as milk fat depression [ 6]. Often, this depression may be up to a 50% reduction in milk fat yield with a greater decline in the de-novo synthesised portion of milk fatty acids [ 7]. Identification of milk fat depression in herds has been based on bulk tank milk analysis where milk fat percentage is < 3.30% and milk protein percentage is a minimum of 3.20% [ 1]. The reduction in milk fat percentage or yield has largely been attributed to a shift in the biohydrogenation of unsaturated FA in the rumen, resulting in the production of milk fat inhibiting isomers of conjugated linoleic acid (CLA), such as CLA t10, c12. Low rumen pH which has been highlighted as a common issue of grazing dairy cows [ 8, 9, 10] is known to disrupt the rumen environment and result in altered microbial processes involved in the biohydrogenation of PUFA’s [ 11]. Low rumen pH in grazing cows has been associated with lower milk fat percentage [ 12]. However, the feeding conditions and interactions with rumen environment required for MFD are not fully understood. Milk fat depression in confinement milk production systems, is often the result of high levels of starch and low levels of NDF in the diet [ 13]. Meanwhile, the occurrence of high water intake, high unsaturated fatty acid (UFA) intake, intense production of volatile fatty acids (VFA) instead of lactic acid and selective feeding behaviour are thought to promote the condition in grazing scenarios [ 12]. Variability in grass composition due to season, weather and grassland management can further intensify challenges in maintaining milk fat levels [ 12, 14, 15]. Benchmarking a decade of holistic agro-environmental studies within the Agricultural Catchments Programme Firkins JL, Eastridge ML, St-Pierre NR, Noftsger SM. Effects of grain variability and processing on starch utilization by lactating dairy cattle. J Anim Sci. 2001;79(suppl_E):E218–38. Ruminant health research – progress to date and future prospects, with an emphasis on Irish research Weld KA, Armentano LE. Feeding high oleic acid soybeans in place of conventional soybeans increases milk fat concentration. J Dairy Sci. 2018;101(11):9768–76.

AOAC, 2005a. AOAC, Method number 960.15. Moisture in animal feed. Official methods of analysis, (18th ed.), AOAC International, Gaithersburg, MD, USA (2005).

The Bord Bia Grass-Fed Standard provides rigorous assurance of Ireland’s commitment to producing dairy sourced only from pasture grazed herds. AOAC, 2005c. AOAC, Method number 990.03. Crude protein in animal feed. Official methods of analysis, (18th ed.), AOAC International, Gaithersburg, MD, USA (2005). The report also found that €1.1bn was invested in dairy processing plants over the past five years, resulting in an additional €340m in wages and profits for the rural economy. That’s something our 1.2 million milking cows can appreciate. And with the national dairy herd due to expand by an additional 300,000 cows in the coming years, there’ll be even more of them to enjoy it, and lashings more fresh milk for us.

But, one thing that will remain constant is our commitment to supplying the highest quality, sustainably produced and naturally tasty dairy products. The grass-fed diet of dairy cattle has a fundamental impact on the taste profile of the milk and subsequent products that are made from it. Ireland’s rich and fertile grazing pastures, coupled with generations of experience and cutting-edge technology and insight, places it in the ideal position to produce an incredibly high-quality and consistent product.”​Dubois M, Gilles KA, Hamilton JK, Rebers PT, Smith F. Colorimetric method for determination of sugars and related substances. Anal Chem. 1956;28(3):350–6. Nitrogen per hectare varied from 159kg in 2022 (12,100kg of grass grown) to 237kg in 2017 (14,000kg grown). At a recent Irish Grain and Feed Association meeting, Professors Finbar Mulligan and Karina Pierce from UCD presented the results of their Lyons Estate research. When the rumen environment is altered, FA including C18:2c9,12 and C18:3c9,12,15 undergo an altered pathway of biohydrogenation and result in the creation of CLA t10, c12 isomers instead of CLA c9, t11 isomers [ 32]. Many studies have attributed the onset of MFD in dairy cows to the presence of the milk fat inhibiting isomer CLA t10, c12 [ 33, 34, 35]. Despite fitting the description of MFD [ 1], milk from LMF herds did not display a higher concentration of CLA t10, c12 compared to milk from HMF herds. Additionally, the correlation between milk fat percentage and CLA t10, c12 for the Entire group was weak and not significant. In agreement with results of this study, many authors have indicated that an increase in ruminal CLA t10, c12 formation does not provide a universal explanation for the reduction in milk fat production during diet-induced MFD and have suggested that other biohydrogenation intermediates of C18:2c9,12 and C18:3c9,12,15 may also be involved [ 32, 35]. For example, average reductions in milk fat percentage and milk fat yield by 52% and 55%, respectively were demonstrated through the use of CLA isomers CLA c8, t10; CLA c9, t11; CLA c10, t12 and CLA c11, t13 [ 36]. Reductions in milk fat yield by 15% were also attributed to the isomer CLA t9, c11 [ 34]. Likewise, reductions in milk fat percentage and milk fat yield by 23% and 21%, respectively were demonstrated using an abomasal infusion containing the CLA c10, t12 isomer [ 37]. Despite this, the only two CLA isomers measured in this study CLA c9, t11 and CLA t10, c12, were not reduced in milk from LMF herds compared to HMF herds. Nor was there any correlation for these isomers and milk fat percentage for the Entire group. It is possible that other CLA isomers linked to MFD such as those discussed above, may have impacted milk fat synthesis in this study. However, no measurements for other CLA isomers were available for our study. Pasture composition: differences with herd milk fat category

Undesirable milk processability characteristics can limit the production of milk products, such as butter or cheese for milk processors [ 26]. Milk processability parameters such as those reported in the current study have not previously been investigated in herds with and without MFD. Our results for milk processability characteristics are similar to other studies for pasture fed cows [ 26, 27] and demonstrated that milk fat percentage had no effect on processability characteristics including milk pH, milk RCT and milk ethanol stability.

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AOAC, 2005b. AOAC, Method number 942.05. Ash in animal feed. Official methods of analysis, (18th ed.), AOAC International, Gaithersburg, MD, USA (2005). Sukhija PS, Palmquist DL. Rapid method for determination of total fatty acid content and composition of feedstuffs and feces. J Agric Food Chem. 1988;36(6):1202–6. Potatoes in Ireland: Sixty years of potato research and development, market evolution and perspectives on future challenges Geographical proximity; strong cultural and social affinities; a shared language; complementary approaches to agriculture and food processing; commonalities in business, law and relationship building; the list goes on. Woolpert ME, Dann HM, Cotanch KW, Melilli C, Chase LE, Grant RJ, Barbano DM. Management practices, physically effective fiber, and ether extract are related to bulk tank milk de novo fatty acid concentration on Holstein dairy farms. J Dairy Sci. 2017;100(6):5097–106.

It has also done extensive research into marine supplements, showing the ways in which various minerals can help with even the most specific conditions, such as osteoarthritis of the knee. Through its trials and research, it provides the collateral that allows both consumer-foods and trade-ingredient suppliers to go to their customers with claims that they can stand over. This figure was driven by the performance of butter, which saw export volumes increase 12%, as well as the strong pricing environment in the cheese market, ensuring exports retained their value, despite a 10% decline in volume. Palmquist DL, Beaulieu AD, Barbano DM. Feed and animal factors influencing milk fat composition. J Dairy Sci. 1993;76(6):1753–71. Rico DE, Preston SH, Risser JM, Harvatine KJ. Rapid changes in key ruminal microbial populations during the induction of and recovery from diet-induced milk fat depression in dairy cows. Br J Nutr. 2015;114(3):358–67.The relationships between pasture and milk components of Irish grazing dairy farms were examined to determine if milk fat percentage was related to pasture composition, milk processability, milk composition or milk FA composition. It is generally accepted that MFD in lactating dairy cows is caused by feeding diets high in starch and low in fibre or by feeding diets high in UFA [ 7, 20, 21]. Furthermore, investigations into the causes of MFD have mainly focused on animals fed TMR diets [ 22]. However, little is known about the relationship between pasture composition and MFD in grazing scenarios [ 1]. Around 80 per cent of Ireland’s agricultural land is given over to grass, and it really is green. Experts from the European Commission’s Joint Research Centre found Ireland’s dairy production is the joint-least carbon intensive in the EU. That is great news for Irish cows – who wants climate change when you have the best cow climate in the world. Pre-grazing herbage mass (above 4 cm) of pasture offered to the HMF herds was similar to the pasture offered to the LMF herds (1821 vs 1660 kg DM/ha). Evidence of the effects of pre-grazing herbage mass on milk fat percentage is conflicting. Some studies have attributed lower milk fat percentages in grazing scenarios to inadequate fibre intake from lower pre-grazing herbage mass [ 1, 8, 12]. Whereas other studies have reported no effect of pre-grazing herbage mass of perennial ryegrass [ 43, 44, 45].It is possible that the effect of pre-grazing herbage mass on milk fat percentage in dairy cows may be different depending on season as NDF content of perennial ryegrass increases throughout the growing season regardless of pre-grazing herbage mass [ 46]. The absence of a difference in dietary fibre content of pasture in the current study was not expected as NDF has been found to have a direct link with milk fat synthesis [ 17, 18]. Acetate, which is a VFA produced from the fermentation of fibrous feeds in the rumen contributes to 50% of milk fat production [ 47]. Hence, a higher dietary fibre content was expected in pasture offered to the HMF herds as a result of the increased milk fat production.