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Animal Management - Elective 2
Analysis of a research paper - Answers
After you have answered the questions provided in Analysis of a research paper you should use these sample answers to check your own.
- What was the objective of this piece of research?
The objective was to compare the effect of four different carbohydrate supplements, of varying rumen degradability, on the productivity and nitrogen utilisation of dairy cows grazing kikuyu pastures.
- Randomisation, replication, control groups (if necessary) and standardised conditions are important elements in any experimental design. Explain how the design of this research experiment satisfies these elements.
The experimental design does satisfy the basic elements of experimental design. Randomisation occurred as 14 cows in early lactation and 6 cows in late lactation were randomly allocated to each of the four treatment groups.
Each treatment was replicated 20 times, i.e. there were 20 cows in each group. There was further replication within groups: 14 cows were in early lactation and 6 cows were in late lactation.
A control group was not necessary because the researchers were looking at the varied effects of different supplements rather than merely the effects of supplements versus no supplements.
Conditions were standardised by:
- matching the cattle according to milk yield (18.0 ± 1.6L/cow/day),
- liveweight (531 ± 7.3 kg) and parity (3.6 ± 1.5 years)
- all groups were fed the same amount of dry matter.
- all groups had a 21 day adjustment period and 35 day experimental period.
- all groups were run together as a herd on the same pasture.
- pasture availability was controlled.
- Discuss how the literature review, carried out by the researchers prior to this research, may have affected the design of this research experiment.
From the study of previous research literature the researchers hypothesised that any improvement in milk production would be dependent upon microbial protein synthesis being limiting. They theorised that microbial protein synthesis may not be limiting during late lactation so the treatment groups contained more cows in early lactation than late lactation.
- Was the data that was collected adequate to formulate conclusions about the effect of the supplements? Explain!
The data collected allowed the researchers to measure nitrogen utilisation by the different treatment groups and the changes in production (milk quantity and quality and cow liveweight changes). The researchers analysed the dietary components of the pasture and the supplements. The total nitrogen intake was calculated from the DOMI and the amount of supplement fed. The excretion of nitrogen was calculated through faecal and milk samples. An analysis of faecal samples for starch indicated where the carbohydrate supplement was fermented. The data collected was therefore more than adequate as it not only allowed the researchers to identify which of the four supplements had the best effect on production but it also gave evidence as to why that supplement gave the best effect, e.g. the researchers were able to conclude that maize, if modified to make it more available to the rumen rather than post-ruminally would probably have an even better effect than the rice supplement.
- Is the presentation of data appropriate? Explain!
The data was presented in tables and by text. The tables were self explanatory however Table 1 would have been easier to read had the dietary components made up the rows and the feed components the columns. Similarly Table 2 would have been easier to read had the treatments formed the rows and the variables the columns. The data from the cows in late lactation was not published and some readers may have been interested to see this data. Graphs may have been useful in summarising results that were significant.
- What conclusions were formed from this experiment?
The researchers concluded that slow degrading carbohydrate sources such as the rice supplement provided better milk responses in cow during early lactation grazing kikuyu pastures. The researchers believed that this was due to the degradation of the carbohydrate being synchronised with the nitrogen available from the fermentation of the pasture. This improved microbial protein synthesis thereby improving nitrogen utilisation. They also concluded that maize grain may prove to be a better supplement if it were processed to improve its fermentation in the rumen rather than post-ruminally.
- Was the General Linear Model (GLM) appropriate to analyse the data? Would a simple t-test, F-test or ANOVA (Analysis of Variance) have been adequate?
The General Linear Model was most suited to analysing data as it takes into account a number of variables including within treatment variations. The t-test is a simple statistical test used to compare two treatment means. The F-test is designed to compare the variance of two treatments. Neither of these two statistical tests would have been suitable for testing the large number of variables that the researchers were interested in. The ANOVA is a simpler form of the General Linear Model and can be used to test the difference between three or more means at one time. The ANOVA however would still not have been a rigorous enough test to consider all the variables required by the researchers to be tested.
- Is there any other information, or results, that may be presented which would improve the adequacy of this research paper?
Photos of the cattle grazing the kikuyu pasture would have been beneficial for comparisons of the visual appearance of the pasture with its chemical analysis. Also the size of the grazing area and the distance from the dairy shed would have given some indication of the energy used by the cattle throughout the day for grazing and travelling to and from milking.
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