Introduction
Cows milked by automatic systems (AS) are most often confined indoors or have access to pasture only during the day in summer. However, grazing allows decreasing feeding costs and improves animal health and welfare. A mobile AS, as described by Dufrasne et al. (Reference Dufrasne, Robaye, Knapp, Istasse and Hornick2010), allowing grazing of dairy cows in fragmented areas is thus advantageous for animals. At grazing, the cows can move more largely than at barn and are submitted to environmental conditions. During heat stress (HS) periods, it is known that feed intake can be reduced, especially with temperature above 25°C or 26°C (Rhoads et al., Reference Rhoads, Baumgard, Suagee and Sanders2013). Little information exists on effects of HS on grazing dairy cows milked by an AS. The aim of this study was to determine the effects of HS periods on the milk yield, milking frequency, fat to protein ratio in milk (F/P) and rumination time (RT) of grazing dairy cows milked by an AS located on pasture.
Material and methods
This study was held at the Experimental Farm of University of Liège (Belgium). A herd of about 50 dairy cows grazed on 18 ha of permanent pastures and was milked by an AS Lely A3 next® (Lely A3 Next, Lely Holding, Maasluis, The Netherlands). The grazing period began in April and ended in October. The cows grazed by strip grazing and two allocations per day were provided. The gate of the AS was manually changed twice per day, at 0600 and 1600 h, to guide the cows onto the next allocation. The cows had to enter the AS to receive the new allocation. In practice, they were fetched for the morning milking, allowing a daily survey of the animals by the herdsman. They had free access to the AS when the gate was changed in the afternoon. Furthermore, they had free access to the AS both day and night.
The temperature humidity index (THI) was calculated according to Ingraham et al. (Reference Ingraham, Stanley and Wagner1979) and was used to define, post hoc, mild HS periods according to Armstrong Reference Armstrong(1994). Consequently, a period of 4 and 7 consecutive days were identified in July (J) and in August (A), respectively. These periods were characterized by a THI>72 during the day and 23.1°C mean temperature. These two HS periods were compared with corresponding normal periods chosen close before and after the period of HS – <9 days – for their similarity regarding the distance from the automatic milking system (AMS) and the availability of water in the grazed paddock. During normal periods, maximum THI was <68 and mean temperature 16.3°C. Water was always available near the AS in a trough (1000 l) and available in some grazed paddocks in individual bowls. Only animals present from the beginning till the end of these periods were taken into account. The total number of lactating cows was 45 in J and 47 in A. The lactation number and days in milk during the normal and HS periods were similar (Table 1). The pastures were composed mainly by perennial ryegrass and white clover. The grass heights were measured by an INRA rise plate meter (INRA rise plate meter, ARVALIS, 37390 La Membroule sur Choisille, France) at each entry and exit in the paddocks. Grass yield was measured with a mower, cutting strips of 10 m long. Grass was sampled at each entry in order to determine chemical composition. Each cow received an amount of concentrate determined with respect to lactation stage. The cows were equipped with a HR-Tag neck collar recording rumination parameters and cow activity (SCR, Netanya, Israel).
Some environmental and animal characteristics during periods of normal and heat stress conditions in lactating cows at pasture (mean and s.d.)
THI=temperature humidity index.
The temperature, THI, distance from the paddock to the AMS, days in milk and lactation number were analysed according to a GLM by using THI conditions (normal and HS) and periods (J and A). Data electronically captured by the AS, that is, milk production, milking frequency, milking visits (result of the sum of milkings, failed and refused milkings), F/P and RT (991 data) were analysed according to a mixed model (SAS, 1999) including THI conditions, periods, lactation number, stages of lactation as fixed effects, and allowing a type 1 autoregressive covariance structure for measurements performed on each animal within THI conditions and periods.
Results and discussion
THI and temperature were significantly different and there was no interaction between THI conditions and periods for environmental parameters (Table 1). The grass composition in CP, NDF, ADF, water soluble carbohydrate (% in DM) and grass digestibility (%) were 16.3, 47.8, 27.3 and 79.7 in J and 19.2, 49.6, 26.2 and 80.6 in A. The grass heights were 10.1 and 8.5 cm at entry and 3.1 and 3.1 cm at the exit, respectively, in J and A, respectively. The grass yield was 1509 and 1437 kg DM/ha in J and A, respectively, the calculated sward availability was 14 kg DM/day per cow. On average, the cows received 1.9 and 2.0 kg concentrate/day during normal and HS periods.
Milking frequency and visits were significantly higher in HS (Table 2). There were significant interactions between THI conditions and periods, the longest periods in A showing no difference between N and HS (1.90 v. 1.98 milking/day and 2.67 v. 2.51 milking visits, respectively). The higher milk production in HS periods can be explained by the increased milking frequency. The cows were attracted to the AS to drink water in the big trough located near the AS during HS periods (unpublished observations). These observations did not confirm Spörndly and Wredle (Reference Sporndly and Wredle2005), who reported no significant difference in milk yield, milking frequency or water intake between a group of cows with unlimited water access and a group with access to water only in the barn. In the present study, with an increase in THI, this behaviour probably increased the number of milking visits and milking frequency.
Daily parameters recorded in cows exposed to normal and mild heat stress at pasture (mean and s.e.)
F/P=fat to protein ratio.
The daily RT was considerably decreased in HS. A reduction of the RT in cows suffering from mild to moderate HS in barns was reported by Soriani et al. (Reference Soriani, Panella and Calamari2013). Decrease in RT is often associated with a reduction in dry matter intake. It seems that, within the conditions of this trial, it was not observed as the milk yield in HS cows was not reduced and was even increased. F/P tended to be lower in HS. This can be related to a diminution in rumen pH explained by a saliva production decrease resulting from RT reduction. Such a decrease in ruminal pH when environmental temperature was increased was also described by Mishra et al. (Reference Mishra, Martz, Stanley, Johnson, Campbell and Hildebrand1970).
Conclusion
It appears from these results that rumination, milking frequency and milk performance of cows milked by an AS are affected by a mild HS at pasture. More studies are needed to study the impact of the length of HS on these parameters.
Acknowledgement
This research was funded by the EU project Autograssmilk SME FP7 314879. The authors thank the DGO3 of SPW (Belgium) for funding the installation of the mobile robot.
Further information
The LiveM International Livestock Modelling and Research Colloquium was hosted by the Basque Centre for Climate Change (BC3) at the Maritime Museum in Bilbao, Spain between 14 and 16 October 2014. LiveM is the livestock and grassland modelling theme of the EU knowledge hub Modelling European Agriculture with Climate Change for Food Security (MACSUR). The MACSUR project is a pilot knowledge hub started by FACCE-JPI in 2012. It provides an opportunity to explore the role and potential of multi-disciplinary networking structures to address complex regional and global issues. More information on MACSUR and the LiveM theme can be found at www.macsur.eu, with PDFs of slides from conference presentations available through the conference website (http://www.livem2014bilbao.com/).
