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Animals, housing and management
The study was conducted from January to August 2021 with 25 female calves (Prim’Holstein, Montbeliarde and crossbred dairy breeds) and nine nurse cows (Prim’Holstein and Montbeliarde), at the Mirecourt – ASTER experimental unit in the Vosges region. The latter has been in Organic Agriculture since 2006 and the animals are exclusively fed with hay and grass. The animals are placed in buildings from November to April. This year, they were taken in the pastures in mid-April. During the period in the building, the cows received an average of 20.5 kg of DM/day including 4.3 kg of DM of Alfalfa-Grass regain (2nd cut) as well as 16.2 kg (of Dry Matter) of permanent meadow hay. The nurse calved between October 2019 and May 2021. The study calves were born between January 9th, 2021 and April 30th, 2021, and remained with their biological mothers for 48 h to assimilate colostrum. They were then placed in a collective nursery, on straw, for a minimum of three days. When two or three female calves were old enough to be adopted and a cow meeting the technicians’ criteria was also available (i.e., subjectively considered docile and that showing mastitis or lameness), then the adoption could take place. Once the family group was formed (i.e. the nurse cow and her adopted calves), (Table 1) the animals were kept together for a minimum of 15 days in a 7*5m stall, half of which was strawed and not the other half (scraped area). Water was available ad libitum, the building was open to the outside, there was no temperature control or artificial light. The family group then joined a second family group for a minimum of 15 days, in a barn identical to the previous one. The nurses grazed for five hours a day (between 11:00 a.m. and 4:00 p.m.), without their calves and according to the weather conditions in order to allow a dietary transition for one week before grazing. Then, the different groups were taken to pasture to form a single herd, composed first of six nurse cows and their respective 16 calves. The pastures were between de 0,64 to 1,41 hectares in size, and had no shelter, but trees lined the sides of the paddocks, providing shade and shelter for the animals. Water was also available ad libitum. The adoptions that took place after mid-April joined the herd on pasture following the same type of procedure (three nurse cows and nine calves). At no time were the cows milked during the study.
In situ observations of the relationship in three sequences between the nurse and the calf
The objective of these in situ observations, under stable conditions, was to characterize the relationship between the nurse and her foster calves. These repeated observations took place in May, August and the last part will take place in October. Scanning samples (all six minutes) were used to record the relative position between members of a family group and their social interactions. Two observers were required, one to scan the cow, the other to scan the calves. A third observer used the focus observation method to detail the calves’ behaviors. The order of the observations of the calves was decided in the field according to the individuals in activity, in order not to observe inactive animals. These observations took place in the morning, around 7:30a.m., and at the end of the afternoon, around 6p.m., in order to observe a maximum of interactions between the animals [53], always during 2 hours.
The data on mutual interactions of the calves was intended to determine the identity of the calf’s primary social partner (respective nurse cow or not) and thus determine a potential attachment of the calf to its nurse and vice versa.
Variables selected during the pasture observations to qualify the relationship between the calf and the nurse and compare it with the variables of the adoption test:
➢ ContactNurseS1 = percentage of SCAN where the calf is seen in contact with its nurse in session 1 (S1).
➢ ContactNurseS2 = percentage of SCAN where the calf is seen in contact with its nurse in session 2 (S2).
Choice/Separation test(Fig. 4)
A « choice » test [52] was used to quantitatively assess the selectivity (behavior preferentially oriented towards the nurse cow) of the calves towards the cows. The session 1 involved the six cows that joined the pasture simultaneously. The session 2 involved the nine cows of the experiment that had time to adapt to their conspecifics. The order of the animals was set to minimize the age difference between the calves and not to put animals that had been together for the « pairing » in the same passage group. Calves ranged in age from one and a half months for the youngest to four months for the oldest. Prior to the test, the calves were separated from their nurse for one hour. In order to comply with the ethical charter, the calves were separated from their nurse for a maximum of 2 hours. The age of the calves for the second test session varied from 4 to 7 months. In both sessions, the choice test was conducted during the day, from 9:00 am to 1:00 pm. Each calf was introduced for five minutes in this setup (closed pen with openings allowing contact between animals, 10 m * 7 m) where the legitimate nurse and another cow from the herd were simultaneously present. Cows were placed in adjacent open pens, also 5 m * 7 m. A final step was the separation test: the removal of the nurse for two minutes. Several criteria related to the calves’ behavior were recorded during the test: the respective times spent with the two cow zones (zones were delimited to facilitate observation) and the number of zone changes, the frequency of interactions with the other cow (sniffing, contact) and the number of vocalizations. As for the cows, their vocalizations were recorded as well as their lighting and licking behavior with the calf and their contact with the grid.
Variables retained in the choice test to qualify the relationship between the calf and the nurse and compare it with the variables of the adoption test:
➢ Time_Nurse_S1 = Percentage of time spent by the calf in the area close to its nurse in Session 1
➢ Time_Nurse_S2 = Percentage of time spent by the calf in the area close to the nurse in Session
To facilitate the understanding of the time spent in each area, a preference index has been used as follows: Preference index = ((time spent in feeder area * 1) + (time spent in other cow’s area * (-1)))/100. The values were distributed from -1 when the calf was mostly in the other cow’s area to +1 when the calf spent a large part of its time in the nurse’s area.
The results of the separation test are presented in Table 4.
At the time of separation from the nurse, the calves will distribute their time in each area more evenly. In session 1, the time spent near the other cow was not different from chance (25%; +/-8.13) (W = 71, P = 0.897) (Fig.7). In session 2, the calf spent an average of 48% (+/-5.56) of its time in the other cow’s area, this difference is significant compared to random allocation (t = 4.796, df = 15, p-value <0.001). So, there is a significant increase in time spent near the other cow between session 1 and session 2 (Fig.7). There was no correlation between the time spent in the nurse’s area before separation and the time spent in the other cow’s area after separation in either session 1 (rs=0.284, df=15, P>0.1) or session 2 (rs=0.088, df=15, P>0.1). Calves vocalized more after separation from the nurse than before separation whether in session 1 (W = 0, df=15, P <0.001) or session 2 (W = 7.5, df=15, P <0. 001) (Fig.8) but did not change area any more regardless of session (session 1: W =15, df=15, P>0.1, session 2: W =51.5, df=15, P>0.1,) nor did they explore differently (session 1: W = 78, df=15, P>0.1, session 2: W = 134.5, df=15, P>0.1,).
There was a significant difference in the frequency of zone change during this separation phase (t = -4.130, df = 16, p-value <0.001) between session 1 and session 2. Calves in session 2 changed zones more times than in session 1. Exploration frequency also increased significantly (Wilcoxon Test; W = 15, p-value = 0.006) between calves in session 1 and session 2.
Table of contents :
Material and Method
1. Animals, housing and management
2. Experimental design
3. Observation of animals
3.1. Adoption
3.2. In situ observation of the grazing introduction
3.3. In situ observations of the relationship in three sequences between the nurse and the calf
4. Behavioral tests
4.1. Choice test (Fig. 4)
4.2. Avoidance test
5. Data analysis
Results
6. Adoption Test
7. Choice Test
8. Separation Test
9. Pasture Observations
9.1. SCAN Results
9.1.1. Session 1
9.1.2. Session 2
9.1.3. Sessions 1 and 2
9.2. FOCUS results
10. Human Test
11. Study of the correlations between the results of the adoption test and the following tests (observation on pasture and choice test)
11.1 Session 1
11.2 Session 2
Discussion
Limitation of the study and perspectives
Conclusion
References
