Milk quality and processability issues exist with milk produced from cows in late lactation and are exacerbated in seasonal systems, where the majority of the herd enter into late lactation at the same time (Phelan et al., Reference Phelan, O'Keeffe, Keogh and Kelly1982). Late lactation milk results in lower manufacturing potential, primarily due to the lack of high quality pasture (Auldist et al., Reference Auldist, Walsh and Thomson1998), as well as physiological changes that occur as lactation progresses (O'Keeffe et al., Reference O'Keeffe, Phelan, Keogh and Kelly1982).
Concentrate supplementation (barley-based) in late lactation has been found to increase milk yield, however, milk fat concentration is reduced (O'Brien et al., Reference O'Brien, Crosse and Dillon1996; McKay et al., Reference McKay, Lynch, Mulligan, Rajauria, Miller and Pierce2019a). Oat grain has several nutritional benefits compared to other cereals like barley, such as a higher lipid and fibre content (Ekern et al., Reference Ekern, Havrevoll, Haug, Berg, Lindstad and Skeie2003) and alterations in the concentrations of fatty acids (Ekern et al., Reference Ekern, Havrevoll, Haug, Berg, Lindstad and Skeie2003) and increases in milk fat concentration (Moran, Reference Moran1986) have been observed.
As cows move later into lactation, tight junctions between epithelial cells in the mammary gland become leaky (Matter and Balda, Reference Matter and Balda2003), which results in reduced milk yield, milk lactose (Stelwagen et al., Reference Stelwagen, Farr, McFadden, Prosser and Davis1997) and an increase in milk somatic cell count (SCC). There is evidence that supplementation with α-tocopherol (α-TOC) improves the structure and function of kidney cell tight junctions (Fusi et al., Reference Fusi, Giromini, Rebucci, Pinotti, Caprarulo, Cheli, Vitari, Domeneghini and Baldi2018) and reduced SCC and the enzyme plasmin which affects the coagulation properties of milk (Politis et al., Reference Politis, Bizelis, Tsiaras and Baldi2004).
The hypothesis of this research was that cows offered an oat grain-based supplement would have improved milk fat concentration due to oats having a higher fibre content. Furthermore, offering cows a high α-TOC supplementation would improve tight junction structure, SCC and milk casein which would subsequently improve milk processability.
Materials and methods
Forty-eight Holstein Friesian dairy cows were blocked on days in milk (DIM) and balanced for parity, milk yield, milk composition and fat and protein kg and SCC. The study was carried out for 49 d at pasture. Cows were assigned to one of four pasture-based dietary treatments in a randomised complete block design (n = 12). The dietary treatments were: pasture (perennial ryegrass) only, control (CTRL); pasture + 2.65 kg dry matter (DM) barley-based concentrate + 350 IU α-TOC/kg concentrate (BARLO); pasture + 2.65 kg DM oat-based concentrate + 350 IU α-TOC/kg concentrate (OATLO) and pasture + 2.65 kg DM oat-based concentrate + 1050 IU α-TOC/kg concentrate (OATHI).
Milk samples were taken once weekly from one successive morning and evening milking from each individual cow. Milk samples from each treatment (n = 12) were pooled into three subsamples (n = 4) which were analysed for milk composition, milk fatty acid profile, RCT and ES. Samples of pasture, feed (online Supplementary Table S1) and standard milk composition (online Supplementary Table S2) were analysed as reported by McKay et al. (Reference McKay, Lynch, Mulligan, Rajauria, Miller and Pierce2019b). Analysis methods for the milk fatty acid profile, RCT, ES, minerals and α-TOC concentration and provided in the Supplementary File.
Statistical analysis
Analysis of data was conducted using Proc Mixed of SAS (2012). The model included the fixed effects of treatment and week and their interaction. The interaction of treatment × time was non-significant in the model and is therefore not reported in this paper (additional information in the Supplementary File).
Results and discussion
Late lactation milk is characterised as having an extended RCT, although this study found that the RCTs of milk (Table 1) from all four treatments (at a natural pH) were similar to that normally observed in mid-lactation milk (4–6 min) (O'Brien et al., Reference O'Brien, Crosse and Dillon1996) and did not display the extreme late lactation characteristics that have been observed previously of 9–15 min (Lucey and Fox, Reference Lucey and Fox1992). This may be because the pasture availability in this study was typical of autumn pasture and was adequate (online Supplementary Table S1) to meet the production requirements of the cows. However, in the current study, milk produced from cows offered OATHI had a shorter RCT compared to OATLO (P < 0.05), which is more suitable for processing (O'Brien et al., Reference O'Brien, Crosse and Dillon1996). To our knowledge, this is the first study that has investigated the effect of α-TOC on the RCT of milk produced from dairy cows.
Table 1. The effect of treatment on milk yield, composition and processability
CTRL, control, pasture only; BARLO, barley-based concentrate + 350 IU α-TOC/kg; OATLO, oat-based concentrate + 350 IU α-TOC/kg; OATHI, oat-based concentrate + 1050 IU α-TOC/kg; RCT, rennet coagulation time; ES, ethanol stability; CLA, conjugated linoleic acid.
abcWithin a row, means with different superscripts differ (P < 0.05).
*, ** and *** are P < 0.05, <0.01 and <0.001, respectively.
Previous research has identified that dietary alterations to increase unsaturated fatty acids (UnSFA) have improved the rheological properties, the spreadability of butter and nutritional properties of milk fat (Pottier et al., Reference Pottier, Focant, Debier, De Buysser, Goffe, Mignolet, Froidmont and Larondelle2006). In agreement, supplementation with oat-grain which is high in UnSFA, resulted in a lower RCT and a higher ES than a barley-based supplement (P = 0.001, P < 0.05 respectively).
The significant focus on the fatty acid profile (online Supplementary Table S3) of milk has been from a human health perspective, as high consumption of SFA has in the past been linked with cardiac issues (Pfeuffer and Schrezenmeir, Reference Pfeuffer and Schrezenmeir2000), while consumption of CLA offers potential health benefits (Koba and Yanagita, Reference Koba and Yanagita2014). Pasture supplementation with oat grain compared to pasture only increased total CLA (P < 0.05), possibly due to the higher concentration of dietary PUFAs (Aro et al., Reference Aro, Jarvenpaa, Konko, Huopalahti and Hietaniemi2007). Increased PUFAs may have encouraged greater rumen accumulation of vaccenic acid, a transient intermediate of ruminal biohydrogenation (Griinari et al., Reference Griinari, Corl, Lacy, Chouinard, Nurmela and Bauman2000) increasing CLA in milk.
While supplementation at pasture with a barley-based supplement increased milk yield, no improvements were observed for the milk processability parameters measured or the milk fatty acid profile. This is in contrast to the additional benefits that can be gained by supplementation with an oat-based supplement as observed in the current study.
In the present study, supplementation with a high level of α-TOC further increased total CLA in milk compared to oat supplementation with a lower level of α-TOC (P < 0.05), suggesting that it either reduced the susceptibility of milk fat to oxidation or that α-TOC altered rumen biohydrogenation (Pottier et al., Reference Pottier, Focant, Debier, De Buysser, Goffe, Mignolet, Froidmont and Larondelle2006). As the present study observed that supplementation with high α-TOC reduced some individual SFA's (P < 0.05), increased cis 9, trans 11 CLA (P = 0.01) and vaccenic acid (P < 0.05), compared to a lower level of supplementation, this suggests that ruminal biohydrogenation was altered by high α-TOC supplementation, similar to a study by Pottier et al. (Reference Pottier, Focant, Debier, De Buysser, Goffe, Mignolet, Froidmont and Larondelle2006). The role of α-TOC in altering rumen biohydrogenation is unclear, but is potentially due to modification of rumen microbes and subsequent fatty acid hydrogenation (Kay et al., Reference Kay, Roche, Kolver, Thomson and Baumgard2005). These authors reported a reduction in plasma urea concentration, indicating a greater rumen ammonia utilisation or reduced ammonia synthesis, which agrees with the current study, as a reduction in rumen ammonia was also observed from cows offered high α-TOC as reported by McKay et al. (Reference McKay, Lynch, Mulligan, Rajauria, Miller and Pierce2019b).
It was hypothesised that a high level of α-TOC would improve tight junction structure and increase milk yield, milk casein concentration and reduce SCC compared to cows offered pasture only based on the findings of Politis et al. (Reference Politis, Bizelis, Tsiaras and Baldi2004), Arreola-Mendoza et al. (Reference Arreola-Mendoza, Del Razo, Mendoza-Garrido, Martin, Namorado, Calderon-Salinas and Reyes2009) and Fusi et al., Reference Fusi, Giromini, Rebucci, Pinotti, Caprarulo, Cheli, Vitari, Domeneghini and Baldi2018. However, the results of this study suggest that poor tight junction structure was not a significant issue, as cows offered pasture only were fed to requirement, had a good milk yield, a normal milk casein concentration and a normal SCC (online Supplementary Table S2), suggesting that pasture quality and availability was adequate for cows to produce good quality milk at 212–261 DIM. Therefore, the good plane of nutrition offered possibly prevented poorer tight junction status and subsequent decline in milk yield that has been previously reported as cows approach the end of the lactation cycle (Fleet and Peaker, Reference Fleet and Peaker1978).
In conclusion, supplementing grazing dairy cows with an oat-based supplement improved milk ES and total milk CLA concentration compared to pasture only. The oat-based supplement also reduced RCT and increased ES compared to cows offered the barley-based supplement. Offering a high level of α-TOC to grazing dairy cows reduced RCT, individual SFA's and increased both total CLA concentration and the concentration of cis 9 trans 11 of late lactation milk compared to the oat-based supplement with a lower level of α-TOC due to possible changes in biohydrogenation in the rumen.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0022029921000091.
Acknowledgements
Funding for this research was provided under the Innovative Dairy Production Systems and Technologies (DairyTech) Innovation Partnership Programme through the Enterprise Ireland Innovative Partnership programme which is co-funded by the European Regional Development Fund (ERDF) under Ireland's European Structural and Investment Funds Programmes 2014–2020. Additionally, the authors acknowledge the contribution of the farm and laboratory staff at UCD Lyons Research Farm and also to Rebecca Mahon for her help in the lab in UCD Belfield.
