Does omission of a regular milking event affect cow comfort?

Abstract

These studies investigate how omission of a scheduled milking event affects indicators of cow comfort. In Study 1, spring calving cows were randomly assigned to one of three milking frequency treatments from calving: twice a day milking (TADAll; n = 14); twice a day, switching to once a day milking at 112 DIM (TAD/OAD; n = 14) and OAD switching to TAD at 112 DIM (OAD/TAD; n = 14). Locomotion ability (ab/aduction, tracking score, speed, head bob, and spine curvature), udder firmness, and milk leakage were assessed weekly for the first 12 weeks of lactation in order to determine initial post-partum differences. Locomotion and udder firmness scores and milk leakage were recorded three mornings prior to, two days immediately after, and one week after the milking frequency switchover. Lying behaviour was recorded for four days using modified voltage dataloggers (Tinytag Plus, Chichester, UK) prior to, during, and after the week of the switch. There was no overall effect of treatment on locomotion scores. TAD/OAD cows showed an increase and OAD/TAD cows a decrease in udder firmness scores on the day after the switch (P < 0.05). The likelihood of a cow leaking milk was higher on the day after the switch (P < 0.05). OAD/TAD cows spent more time lying than TAD/OAD cows on the day of (P < 0.05) and on the day after (P = 0.1) the switch. In study 2, spring calving cows (n = 36) were randomly assigned to three treatments, two of which were used for the study: milked either 14 (14×) or 13 (13×) times weekly. 13× cows were not milked one evening each week. Lying behaviour was recorded on the day prior to, the day of, and the day after the omitted evening milking for 2 consecutive weeks. Udder tension and milk leakage were recorded the morning of the day of and the day after the omitted evening milking for three consecutive weeks. On the day of the omitted milking, 13× tended to have shorter lying bouts than 14× cows (P = 0.1), and tended to spend less time lying/hour than 14× cows, particularly 13 to 24 hours post milking (P = 0.06). On the day after, 13× cows had higher udder tension scores (P < 0.001), and a higher incidence of milk leakage (P < 0.001) prior to milking than 14× cows. In both studies changes in behaviour and udder tension were transient. Thus the practice of reducing milking frequency from twice to once daily in mid lactation, or omission of a weekly milking event, is unlikely to be a significant welfare problem for dairy cows.

Introduction

Cows in pastoral dairy systems are usually milked twice a day (TAD) for the entire lactation. However, there is growing interest amongst producers in once a day milking (OAD) because of its compatibility with off farm employment, and reduced labour and cost. This practice obviously means less milk is produced (Remond et al., 2004) but there are positive implications for several other production parameters (improved liveweight, milk composition and reproductive performance; O'Brien et al., 2005, Clark et al., 2006, Ferris et al., 2008). It also does not appear to cause major welfare problems for cows compared with TAD milking (Gleeson et al., 2007, O'Driscoll et al., 2010a, O'Driscoll et al., 2010b) although cow locomotion can be impaired due to the discomfort of a distended udder, in particular at the beginning of the lactation (O'Driscoll et al., 2010b). Thus OAD milking at the beginning of the lactation may pose a particular welfare problem for high yielding cows.

An alternative management strategy that could combine the positive implications of both TAD and OAD milking, is to milk cows TAD at the beginning of the lactation and then switch to OAD milking once peak lactation has passed. O'Brien et al. (2006) reported that the persistency of the lactation curve for milk yield was greater for cows milked OAD than TAD. Moreover, there is a critical time during early lactation when frequent milking elicits a carryover effect of increased milk production for the remainder of the lactation (Dahl et al., 2004), probably due to increased mammary cell proliferation (Hale et al., 2003). Thus the reduction in milk yield due to OAD milking, when implemented later in lactation, is probably less than when employed from the start of lactation. Milking cows TAD when milk yield is increasing is also likely better for cow welfare than OAD milking, because pressure in the udder is reduced at each milking event. Later in the lactation, when milk yields are lower, OAD milking permits the cow greater control over temporal behaviour patterns (O'Driscoll et al., 2010a), and reduced time spent walking on farm tracks could have positive implications for hoof health (O'Driscoll et al., 2010b). This practice also reduces the necessity for additional labour units on the farm once the busy calving period is over.

Another potential strategy to reduce labour input on farms is to milk cows 13 times (13×) instead of 14 times (14×) weekly. 13× weekly is of interest to smaller producers as it facilitates one free morning or afternoon each week. However, abrupt and frequent changes between different milking frequencies could cause discomfort for the cow arising from intramammary pressure. Milk yield is locally regulated by the udder (Wall and McFadden, 2007), and is a function of mammary cells and their metabolic activity (Stelwagen, 2001). Short-term effects on milk secretion as a result of a change in milking frequency are probably caused by up or down regulation of cellular activity, whereas longer term effects are thought to be due to changes in cell number (Stelwagen, 2001). Thus cows milked TAD at the beginning of the lactation will probably have greater proliferation of mammary cells than OAD milked cows. These cows would therefore accumulate more milk in their udders between milkings after a switch to OAD milking, than cows milked OAD from the beginning of lactation and this could be a source of discomfort.

For cows switched between OAD and TAD milking on a regular basis the source of this discomfort is likely to arise from what Knight et al. (1998) identified as ‘the acute phase’. This is the first of three distinct phases through which the mammary gland evolves in response to a change in milking frequency. This phase is characterised by acute regulatory mechanisms such as feedback inhibition of lactation, tight junction leakiness and the onset of apoptosis and lasts for between 1 and 2 days. Cows milked 13× weekly would experience ‘phase 1’ on a weekly basis, and thus regular adoption of this practice has the potential to result in chronic discomfort for the cow.

This paper presents findings from two studies that were carried out to investigate how a change in milking frequency can affect indicators of dairy cow comfort. Study 1 involved cows that were assigned to either OAD or TAD milking at the beginning of lactation, through a switch in milking frequency at approximately 112 DIM. Locomotory ability, udder firmness and milk leakage were monitored from the beginning of lactation for 12 weeks and during the ‘switch period’ (i.e. 112 DIM ± 7 days), as well as lying behaviour during the switch period. We expected that cows milked TAD in early to peak lactation would have better locomotion, lower udder firmness scores, and less milk leakage than OAD milked cows. However, we also expected that cows switched from TAD to OAD milking would have impaired locomotion and high udder firmness scores during the switch period, in comparison to cows that continued to be milked TAD. We also expected that they would lie less during this period, due to udder discomfort. In order to determine whether these changes were due to a change in management routine per se, or due to the directionality of the change in milking frequency, we also investigated the same measures in cows switched from OAD to TAD milking at the same stage of lactation.

Study 2 investigated the effect of 13× weekly milking on lying behaviour, udder firmness, and milk leakage. We expected that missing a milking event would result in less lying behaviour, and increased udder firmness and milk leakage in cows on the day following the missed milking.