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CASE NOTES

A trial of treatment options for feedlot lambs

Belinda Edmonstone, DV Lachlan LHPA and Greg Curran, Technical Specialist (Western Division), Broken Hill I&I NSW

Posted Flock & Herd March 2011

Introduction

A lamb feedlot operator was considering how best to prepare and support lambs being feed lotted. He approached Lachlan LHPA for assistance. It was agreed that the best approach would be run a trial to see how lambs responded to each treatment regimen, and assess changes in bodyweight and financial returns. Sponsorship by a supplement provider allowed laboratory assay of key minerals and Vitamin B12, to help better understand any responses.

AIM

To determine the impact of 3 treatment regimens (vaccination, mineral and

vitamin supplementation) on growth rate of feedlot lambs and financial returns.

METHOD

A consignment of approximately 400 cross bred lambs was inducted into the feedlot.

They were randomly allocated into a control group and two treatment groups with 100 head in each group. The lambs were individually identified with numbered ear tags; weighed; and treated according to their respective regimen. The three groups had similar bodyweights.

Blood samples were taken from 12 animals in Group 1 and 2 and analysed for selenium, zinc, copper and Vitamin B12 before the trial and at the end of the trial. No animals were deficient in any of these trace elements or minerals (appendix 1).

The three treatment groups were:

Group 1 –Control group. Ear tag colour PURPLE.

These lambs were treated with the feedlots standard protocol.

Group 2 – Treatment group 1. Ear tag colour RED.

These lambs were treated with the feedlots standard protocol plus Maximin administered orally with the drench:

Group 3 – Treatment group 2. Ear tag colour GREEN.

These lambs were treated with the feedlots standard protocol. However they were given a Glanvac6 plus B12 instead of the standard 5 in 1:

The lambs were reweighed a month later and these individual weighs recorded for comparison against their induction weights. 

The lambs were also categorised into different weight ranges of sheep 'smaller' than 38.3Kg and sheep 'larger' than 38.3kg and the response to treatment compared.

RESULTS

At the end of the trial, all 3 treatment groups had similar bodyweights and weight gains (table 1). Changes in bodyweights over the trial were not statistically different (ttest).

Table 1 : Average Bodyweights for Entire Group (Induction; End; Gain)
  PURPLE RED GREEN
Induction 42.1 41.2 41.4
End of trial 49.2 48.9 49.2
Gain over trial 7.1 7.7 7.8

Average weight gain for all 300 sheep in the trial was 7.51kg, or a gain of ~250 grams per day during the trial period. Sheep gained an average of 18.3% of their initial bodyweights; the average initial bodyweight was 41.6kg.

These initial results suggested that the 3 treatments had made no difference to the sheep. The sheep were then categorised into different weight ranges and compared (table 2). Sheep of different bodyweights responded differently to treatments.

Table 2: Weight gain for sheep of different induction weights (kg)
Average weight gain PURPLE (number) RED (number) GREEN (number)
Sheep 45kg and greater 6.3 (21) 7.8 (20) 6.7 (24)
Sheep 36-44kg 7.4 (74) 8.1 (68) 7.7 (66)
Sheep 35kg or less 7.2 (5) 5.7 (12) 10.3 (10)

The greatest single bodyweight gain was found in the 10 sheep in the (35kg and less) GREEN group treated with (First Mectin with Selenium, Glanvac6 with Vitamin B12, and Vitamin ADE supplement).

To be able to test whether sheep were responding to treatments, it was important to split them into two classes (Smaller/Larger). It was found that 38.3kg best discriminated between responses to treatments across all treatments, while giving sufficient numbers for statistical testing.

Sheep classed as 'smaller' (under 38.3kg at first weighing: 70 head) had a higher weight gain proportional to their initial bodyweight (GainPC - 20.4%) than 'larger' sheep (GainPC - 17.7%), which was statistically significant (ttest – probability: 0.012).

Bodyweight changes, and bodyweight change proportional to initial bodyweight, in smaller and larger sheep were then examined for each of the 3 treatments (Table 3 and Figure 1).

Table 3: Weight gain and % weight gain by size and treatment
  Treatment Average Wt Gain (kg) SD* Average % Wt Gain SD* Number Comments
38.3 kg & over GREEN 7.51 2.99 17.6% 0.072% 80 Medium weight gain
PURPLE 7.06 3.11 16.3% 0.074% 80 Least weight gain
RED 8.30 3.25 19.3% 0.081% 70 Highest weight gain
All 7.59 3.14 17.7% 0.076% 230 Variation less than for smaller sheep
Under 38.3 kg GREEN 8.46 2.97 24.2% 0.092% 20 Greatest % gain
PURPLE 7.41 3.53 20.3% 0.094% 20 Medium % gain
RED 6.34 4.61 17.9% 0.137% 30 Lowest % gain; greatest variation
All 7.25 3.95 20.4% 0.115% 70 Variation greater than for larger sheep
SD*: Standard Deviation (measure of variation in group)
Figure 1: Treatment effects on larger and smaller sheep
Graph of treatment effects

The 3 treatments administered had different effects on bodyweight in smaller and larger sheep.

For the smaller sheep:

For the larger sheep:

contrast to the smaller sheep where RED treatment gave smallest GainPC

Discussion

On the basis of this trial it is recommended that sheep feedlot producers consider the varied ways sheep of different size may respond to different forms of supplementation. By working with professional advisers and undertaking a simple trial producers may be able to more confidently select products that will increase growth rates and profitability in their enterprise.  The results of this trial can be further discussed in terms of the response to treatments, basis for the responses to treatment, financial implications, weaknesses of trial design and implications of the trial and its analysis.

Response to treatments

Sheep in the 'smaller' group responded differently to treatments than sheep in the 'larger' group. Treatment responses were complex and open to various interpretations, largely because of the mix of supplements and preventives in each treatment group. Treatment components are summarised in Table 4.

Table 4: Treatment components
Group Drench* Selenium* Maximin ADE Vx B12*
PURPLE 12.5ml 1   2ml 5-in-1  
RED 12.5ml 1 11.5ml 2ml 5-in-1  
GREEN 12.5ml 1   2ml Glanvac 1
  * First mectin * in First Mectin       * in Glanvac

Treatments:

*  PURPLE  5-in-1; no Maximin; First Mectin with selenium; Vit ADE, no B12

*  GREEN  Glanvac + B12; no Maximin; First Mectin with selenium; Vit ADE

*  RED  5-in-1; Maximin; First Mectin with selenium; Vit ADE; no B12

Basis for responses to treatment

Possible explanations for different responses to treatments between larger and smaller sheep were:

- Vitamin B12 (cobalt) deficiency caused failure to thrive and grow. If the lighter lambs were lighter because of Vitamin deficiency then supplementation should have a positive effect. However the blood results from their cohorts do not reflect any deficiencies (appendix).

- Supplementation of the lighter lambs with Vitamin B12 had a positive impact as their rumen was not fully developed and producing adequate B12 from cobalt. (Maximin delivered a high dose of cobalt (38gm) compared with Glanvac 6 B12 containing a dose of 2mg of hydroxocobalamin). The CLA vaccine had a positive effect on the lighter age group.

- Glanvac+B12 in GREEN treatment benefited smaller sheep more than larger; this benefit might come from either protecting smaller sheep from CLA or supplementing them with B12. As Maximin in the Red treatment added cobalt, a precursor for B12, protection from CLA might be more important than adding B12

- Maximin appeared to benefit larger sheep, but may have had deleterious effects when given to the smaller group. The possible deleterious effects of Maximin might be explained by its selenium adding to selenium given with First Mectin

Assays of selenium (GHS PX), Vitamin B12, copper, and zinc of 10 sheep (7 smaller, 5 larger) at the start and end of the trial are given in the Appendix, with commentary. This assay did not allow any conclusions to be reached about the roles of Vitamin B12, selenium or vaccines in bodyweight changes observed, but gave some indication of their effects.

The larger proportional bodyweight gains in smaller sheep were related to their greater capacity to grow than any treatment effect. This is confirmed on regression analysis of GainPC on size and treatment. Treatment had no significant effect on GainPC (probability: 0.78) while size was statistically significant (probability: 0.023). The regression co-efficient for size indicated that being in the larger group reduced GainPC by 2.7%, when allowing for any treatment effect.

Financial implications of treatments

If sheep liveweight was valued at $3 per kg, then sheep in the trial gained an average value of $22.53 per head during the 4 weeks, a total of $6759.

The comparative differences in bodyweights or % gain between treatments were small but important. Significant financial gains were possible depending on treatment chosen:

The estimated returns on selecting the best over the least effective treatments for smaller and larger sheep were:

o If bodyweight was valued at $3 per kg, then the extra value created by the best treatments over the least effective was 433.60kg * $3 = $1300.80, or $4.34 a head

Weaknesses of trial design

- Not having an untreated control group meant that it was not possible to estimate the effect of each component treatment on bodyweight change.

- Sample sizes were too small to test whether a component of a treatment was important.

Implications of the trial and its analysis

Although initially none of the treatments appeared to any significant impact on growth rates, analysis found a complex mix of responses to treatments depending on whether sheep were classed as smaller or larger, about an initial bodyweight criterion of 38.3kg.

These responses were clear and large enough to justify the cost and effort of trialling different treatments. The trial and its analysis allowed the feedlot operator to estimate cost-benefits for each treatment regimen. The feedlotter changed treatment regimens as a result of the trial, to include Glanvac with Vitamin B12.

If a feedlot operator had run this trial and adopted the best set of options found over the least effective, this decision would have gained $1300 during the trial, or $4.34 a head. This compares with $6759 in value in bodyweight gain across all 300 sheep during the trial, or $22.53 a head.

The complexities found in this study suggest that this operator would benefit from professional assistance in designing the trial, as well as analysing and interpreting its results.

The clear differences in response, and the greater size of responses in the smaller group, could justify drafting off a smaller group by bodyweight, and giving different treatments to smaller and larger groups.

Repeating this trial would be useful, as there were significant and important bodyweight and financial gains found that could be related to treatments. The complexities in treatments; responses by bodyweight group; and their interpretation mean that replicating the trial might produce different results in different sheep or from different backgrounds. Further work to understand treatment responses are likely to be needed.

Analysis and interpretation of trials can be more complex and difficult than doing the trial. The trial demonstrated the value of a district veterinarian conducting work to examine which veterinary treatments were most effective in a local livestock production setting, and be in a position to explain why. The trial also showed the value of collaboration between a district veterinarian and others with expertise in analysis and feedlot management.

This paper and presentation allows the work to be recorded, discussed, and referred to by others working with feedlot sheep in future, or using similar treatments. The findings raise questions that could be answered with further trials, and more specific investigations.

Acknowledgements

Chris Sweeney manager of 'Amarina Feedlot', Forbes for his contribution in providing the facilities and livestock.

Thank you to Virbac for their support in this trial.

APPENDIX - BLOOD TEST RESULTS AND Discussion

Bloods submitted: 5.5.06

* Smaller: <38.3 kg induction bodyweight  Larger>38.3kg induction bodyweight

SAMPLE GSH PX COPPER ZINC VIT.B12 Size*
  (50 to 550) u/gHb (7.5 to 20.0) umol/L (7.0 to 25.0) umol/L (400 to 5000) pmol/L  
1 584 H 20.6 H 10.9 2067 Smaller
2 433 16.1 12.8 741 Larger
3 228 18.1 13.2 3487 Larger
4 212 17.6 15.0 783 Smaller
5 157 21.6 H 11.8 1569 Smaller
6 338 23.8 H 10.5 2127 Larger
7 186 16.1 11.8 2087 Larger
8 268 15.5 10.8 1444 Larger
9 326 13.5 10.0 1196 Smaller
10 495 17.6 15.1 1509 Smaller
11 458 19.1 11.8 1936 Smaller
12 494 15.5 12.8 1305 Smaller
Note: no deficiencies of selenium, copper, zinc, vitamin B12

Bloods submitted: 6.6.06

SAMPLE GSH PX COPPER ZINC VIT.B12 Size* Treatment
  (50 to 550) u/gHb (7.5 to 20.0) umol/L (7.0 to 25.0) umol/L (400 to 5000) pmol/L    
1 690 H 12.4 15.2 2808 Smaller Red
2 635 H 14.1 14.4 1754 Larger Red
3 481 14.9 12.6 1058 Larger Red
4 584 H 16.9 15.1 1362 Smaller Red
5 504 18.8 14.2 2215 Smaller Red
6 576 H 18.4 11.8 2834 Larger Red
7 460 16.9 16.5 2545 Larger Purple
8 468 12.4 12.4 1285 Larger Purple
9 422 15.7 12.1 1889 Smaller Purple
10 639 H 13.3 17.3 1434 Smaller Purple
11 681 H 16.3 14.0 2957 Smaller Purple
12 612 H 14.5 12.6 2580 Smaller Purple
* Smaller: <38.3 kg induction bodyweight, Larger>38.3kg induction bodyweight

Note 1: no deficiencies of selenium, copper, zinc, vitamin B12

Note 2: above normal range GSH PX levels in 4 Red and 3 Purple sheep (5 smaller; 2 larger)

Change in Biochemistry between Induction and End of Trial

Parameter GSH PX COPPER ZINC VIT.B12 Weight Gain*
Normal range (50 to 550) u/gHb (7.5 to 20.0) umol/L (7.0 to 25.0) umol/L (400 to 5000) pmol/L (kg)
All 214.4 -3.8 0.5 372.5 8.1
RED 253.0 -3.7 1.4 209.5 10.6
PURPLE 175.8 -3.9 -0.4 535.5 5.5
Smaller sheep 205.5 -4.8 1.8 698.4 7.7
Larger sheep 232.3 -1.9 -2.1 -279.3 8.8
* weight gain for 12 sheep sampled

Discussion of blood tests

 

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