Dam Van Tien
This study was undertaken to determine whether a food not previously ingested by weaned (6 month old) goats (i.e. rice straw), would be ingested sooner if their mothers had eaten rice straw in the 3 weeks before weaning. An attempt was made to determine whether this familiarity with rice straw was transferred from mother to offspring by way of her milk, or by social transmission, i.e. by kids observing their mother when she ingested rice straw.
Previous experience gained by kids by either of these two mechanisms shortened their period of non-ingestion of rice straw from about 10 days to less than 6 days after it was first offered in the post-weaning period. The learning via mother’s milk tended to be slightly more effective than learning by observation, but the combination of both mechanisms, as occurs in nature, was more effective than either alone.
It was concluded that learning from mother before weaning affects the subsequent acceptability of foods and the time taken for those foods to be ingested when offered later in life. Pre-weaning training provides a strategy for reducing food neophobia and promoting the intake of supplementary feeds by livestock in the post-weaning period.
Maximizing food intake in farm livestock leads to higher rates of production and generally greater economic efficiency. However, when farmers try to achieve maximum production, they may find that the foods they make available to their animals, and believe are nutritious, are not readily eaten by them. For instance, Vietnamese Bachthao goats took 40 days to adapt to and start to ingest rice straw given to them for 15 min in the early morning (Tien and Ha, 2000). This non-ingestion of foods when they are first offered to goats is due to neophobia (fear of novelty) (Shortens 1954, cited by Nolan 1996) but the neophobia can be reduced by familiar surroundings and the presence of food cues that are familiar to the animal.
Experience of foods is essential if young animals are to become familiar with them and quickly adapt to eating them in their post-weaning feeding environment. Ruminants use their senses (sight, smell, taste and touch) to differentiate among foods and they may learn about a food’s sensory characteristics from their mother during the pre-weaning period (Provenza and Balph, 1987; Provenza 1994, 1995). Thus, mothers can train their young to avoid harmful foods, and to select nutritious novel alternatives (Mirza and Provenza, 1994). Learning in the absence of a mother or other social teacher may be slower and less effective.
It has been suggested that foods ingested by mother influence the flavor of her milk, and the flavour becomes familiar to their offspring and affects their preference for similar foods in their later life (Morrill and Dayton, 1978; Nolte and Provenza, 1992). Thus, the food preferences of young livestock may be conditioned before they start to ingest solid foods. It is currently thought that learning from mother can be achieved indirectly via mother’s milk or when the offspring observes its mother eating foods that it has not previously experienced, but there is no information to indicate the relative importance of these to mechanisms. In this study we hypothesised that learning from mother involves both, ‘learning by observation’ and ‘learning via mother’s milk’ and we tried to determine the relative importance of both.
The experiment was conducted in Trihai village, Ninh Thuan province. Twenty-four kids born to Bachthao goats that had never been offered rice straw were used. The kids’ learning about rice straw in the last three weeks before weaning, at three months of age, was determined by testing their intake of rice straw in a daily 20 min test at six months of age. These tests were made on four groups of kids in the absence of their mothers. Preparation of the groups was as follows:-
‘Learning from observation’ group (LO): Rice straw was offered to mothers in the presence of their kids for 20 min each day during the last three weeks before weaning. Just before the kids were put with their mothers, they were given as much milk as they would drink (from a surrogate mother not given rice straw in her diet). The kids in this group were separated from their mother at all other times during the day.
Learning from mother’s milk’ group (LM): Rice straw was offered to mothers without their kids present for 20 min each day during the last three weeks before weaning. (This was done in order to prevent the kids from learning about rice straw by observing their mothers’ behaviour). The kids grazed with their mothers for the remainder of each day.
Combination of learning from both observation and mother’s milk’ group (LOM): The mothers of kids in this group were offered rice straw with their kids nearby for 20 min each day. The kids grazed with their mothers for the remainder of each day and could suckle at any time.
Control group (C): The mothers of kids in this group were not offered rice straw while they suckled their kids. (The kids in this group had neither direct or indirect experience of rice straw).
All mothers in the LOM, LM and LO groups were given rice straw for 21 days in the 3 weeks before weaning. After an overnight fast in the holding pen, kids in these groups were present in group pens with their mothers when the mothers were offered rice straw, but in the LO group the mothers were offered rice straw in the absence of their offspring. The kids could reach the rice straw and could participate in the ingestion of straw. Each morning, each mother was offered at 500 g rice straw at the start of a 20 min period. After each morning’s training, mothers were put onto rangeland with their kids (except for the LM group) according to the traditional method of feeding goats in this region.
At 6 months of age (i.e. 3 months after weaning) all the kids were tested to determine their voluntary intake of rice straw in a daily test lasting 20 min. Before the test, animals were exposed to the testing environment and routine for 3 days. Sham testing was done using local native grasses that were familiar to the goats: rice straw was not introduced at this time. From 5:00 to 5:20 hours, after an overnight fast in the holding house, 6 goats in the LOM group were placed in the test area containing 6 feeders (each kid having its own feeder but being able to observe the other kids being tested in its group. The LM, LO and C groups were tested successively from 5:30 to 5:50, 6:00 to 6:20, 6:30 to 6: 50 hours, respectively. The test period for each treatment was kept constant because it avoided errors.. Each group was offered rice straw only during the test periods. The intake of rice straw by individuals in all groups during the 20 min was measured daily and the testing was continued for 21 days. Each morning after the tests were completed, the feed containers were thoroughly cleaned, rinsed and air-dried and the goats were put out to graze together for about 8 h.
Analysis of variance was performed using the general linear model (GLM) procedure of Mintab version 12 (1998). Comparisons with a confidence level of 95 % were used to determine the effects of behavioral treatments between groups.
The results given in Figure 1 and Table 1 indicate that animals in the LM group started to ingest rice straw on Day 4 whereas the inexperienced goats in the control group totally rejected the feed until Day 10. The animals in the LOM and LO groups started to eat the rice straw on Day 4 and Day 5, respectively. There was no difference in intake between goats in LM and LO groups in the first week of testing (P<0.3) except on Day 5.
Figure 1: The intake (g/animal) of rice straw during a daily 20-min test of goats with no opportunity to learn about rice straw (Control) or experience of rice straw obtained by observing their mothers eating it (LO), with possible indirect experience of rice straw via mother’s milk (LM), or with a combination of both LO and LM (LOM). Results are shown as means for six goats per treatment.
During the second week, there was a significant (P<0.01) difference in intake between them except on Day 8 and Day 12. Animals in the LOM group ingested more supplement than those in the remaining groups during the first two weeks of test (P<0.01). There were no other significant differences in intake among the LM, LO and LOM groups during the last week of testing when intake during testing appeared to have reached a plateau value (Week 3).
Table 1. The intake (g/animal) of rice straw during a daily 20-min test by naďve goats (Control) or goats either experienced by observing their mothers eating it (LO), via mother’s milk (LM) or with a combination of both LO and LM (LOM). Results are shown as means ± SD for six goats per treatment.
|2||0||0||15.6 ± 1.1||0|
|3||0||0||23.2 ± 2.0||0|
|4||16.0 ± 2.3||0||27.3 ± 1.8||0|
|5||23.2 ± 3.1||0||43.8 ± 2.4||19.0 ± 2.1|
|6||27.7 ± 3.1||0||50.0 ± 3.4||25.7 ± 2.4|
|7||44.2 ± 4.3||0||67.5 ± 4.3||35.3 ± 3.1|
|8||50.0 ± 3.8||0||80.8 ± 5.2||45.8 ± 3.3|
|9||67.3 ± 5.1||0||96.7 ± 6.4||50.3 ± 3.4|
|10||81.3 ± 4.8||0||95.2 ± 5.4||68.3 ± 4.3|
|11||95.0 ± 4.1||3.7 ± 0.3||83.5 ± 6.3||83.0 ± 3.7|
|12||94.3 ± 5.7||12.5 ± 1.5||86.0 ± 5.7||95.0 ± 4.3|
|13||83.7 ± 4.3||22.5 ± 2.1||91.7 ± 4.9||94.5 ± 5.1|
|14||85.5 ± 4.8||28.5 ± 2.8||94.5 ± 5.4||83.5 ± 6.3|
|15||91.2 ± 6.1||41.5 ± 3.6||93.3 ± 4.7||86.0 ± 5.0|
|16||94.2 ± 5.7||48.5 ± 4.5||84.7 ± 5.3||91.7 ± 4.5|
|17||94.0 ± 4.6||65.3 ± 4.0||88.2 ± 6.4||94.3 ± 3.9|
|18||84.7 ± 4.9||77.0 ± 5.1||92.7 ± 5.1||93.3 ± 4.6|
|19||87.4 ± 5.7||91.7 ± 5.4||94.3 ± 4.8||84.7 ± 4.8|
|20||88.8 ± 6.0||90.8 ± 6.1||93.3 ± 5.1||88.1 ± 5.3|
|21||92.2 ± 5.1||83.5 ± 4.8||84.7 ± 4.2||92.7 ± 4.8|
Before weaning, most livestock species are initially very dependent on their mothers for food protection. The mother also has an important role in assisting their offspring to learn about foods that they may encounter in the future. The main purpose of this study was to investigate the latter capacity.
As indicated in Figure 1, all kids that had direct or indirect experience with rice straw before weaning ingested more of it than animals in the control group (P<0.01) during the post-weaning testing period. All animals in the LOM group, with the potential to learn both via both mother’s milk and by observation, ingested more rice straw than animals in the LM and LO groups (P<0.01) and reached their plateau intake (96 g/day) about 2 days earlier than the latter groups. These results suggest that learning from mother probably occurred via two separate mechanisms: (i) learning by developing familiarity with cues (flavor) in mother’s milk (Galef 1974); and (ii) learning by observing mother ingesting foods. Both these mechanisms, alone and in combination, seem to affect the time taken for animals to take at least a small amount of the novel food. Once an animal ingests a small amount of a novel food, feedback from the digestible nutrients is also an important determinant of preference for, or subsequent avoidance of, foods. This personal experience can extinguish a food preference acquired from the mother. In this connection, Provenza et al (1993) found that, if a lamb experiences mild toxicosis from eating a nutritious feed its mother prefers, the lamb will acquire an aversion to the feed even though it sees its mother still eating it avidly.
It has been shown with rats that mothers can influence the diet preference of their offspring by the presence of flavour cues in their milk (Galef and Sherry 1973). The role of mother in passing on information about foods has been studied in ruminants with contradictory conclusions. Chapple and Lynch (1986) found that lambs that had been reared with their mothers ingesting wheat (and had the opportunity to ingest it themselves) accepted wheat more readily when next offered wheat post-weaning, whereas lambs removed from their mothers at birth and reared in a pen on bottled milk with wheat available to them did not eat any wheat in a 5-day post-weaning test. In contrast, Thorhallsdottir et al (1990) concluded that lambs did not learn to eat novel foods when observing, but not concurrently ingesting those foods, while social models (mother, another ewe) ate those foods. The results of previous experiments and the present study tend to strengthen the idea that learning about specific foods is more effective when observation of a teacher occurs in combination with the opportunity for the learner to participate in the feeding activity.
The present study of the transmission of information about foods when an offspring is being suckled does not eliminate the possibility that the kids were learning by detecting residual food around the mouth of the mother or via odours in expired gases that arise from fermentation of the rice straw eaten before the kids were re-united with their mothers after their absence when their mothers were eating rice straw.
Transmission of diet flavor from a mother to her offspring via milk is an important component of learning from mother. Learning by observation of mother ingesting foods (and having the opportunity to mimic the activity) together with learning via cues in mother’s milk establishes a food preference for livestock that helps them to adjust to their food environment after weaning.
In goats, learning via mother's milk could reduce the time required by weaned kids to fully accept and ingest a newly offered food (rice straw) by about 7 days. This finding may provide the basis for devising management techniques allowing better use of agro-byproducts as supplementary foods for small ruminants and pave the way to improve animal productivity and to increase income of poor farmers.
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