Ovine Observer

Feeding unsalable carrots in total-mixed rations for lambs

Daniel Forwood (UQ), Louwrens Hoffman (UQ), Alex Chaves (USYD) and Sarah Meale (UQ)
Author correspondence: d.forwood@uq.edu.au

Introduction

Food waste is estimated to cost Australians $20 billion per year. Vegetables comprise approximately 29% of total food wastage, with one-third of carrots produced in Australia being discarded due to aesthetic standards set by industry.

Fresh carrots are an energy-dense feedstuff comprising approximately 13.76 MJ metabolisable energy/kg dry matter and 10% crude protein. Therefore, an opportunity exists to use carrots that do not meet industry aesthetic standards in livestock rations.

However, fresh carrots have not previously been fed to ruminants as a total-mixed ration (TMR). Therefore, the impact of including carrots in a lamb TMR on lamb performance, carcass and meat quality is not known. Carrot total mixed ration

The objective of this study was to determine the influence of a TMR including unsalable carrots on lamb performance as measured through live weight gain, carcass characteristics including hot carcass weight, subcutaneous fat depth, and meat quality attributes including meat and fat colour. It was hypothesised that feeding carrots in a TMR would have no effect on these traits.

Carrot total mixed ration

Materials and methods

Thirty-six 7-month old Merino wether lambs were randomly allocated to one of two diet groups- control or carrot TMR, with both groups balanced by live weight (24.7±0.3 kg LW). The lambs used in this study were cared for under the approval and guidance of The University of Queensland Animal Ethics Committee (AE59549), in accordance with the Animal Care and Protection Act (2001). The dry matter (DM) composition, predicted metabolisable energy and protein content of each TMR are shown in Table 3.

 *Predicted values determined using the Small Ruminant Nutrition System (Texas A&M University)

Lambs were individually-housed for the feeding experiment to capture individual feed intake (g DM intake per day). The lambs were adapted to their allocated diet for 14 days before being fed this same diet ad libitum for an experimental period of 11 weeks leading up to slaughter. Lamb live weights were obtained weekly prior to feeding.

At 10-months of age, lambs were slaughtered at a commercial abattoir. Hot and cold carcass weight were measured on each lamb. Subcutaneous fat depth, eye muscle area and meat quality attributes were measured on the chilled loin muscle (Longissimus dorsi et thoracis) 24 hours post mortem and included ultimate pH, meat colour, fat colour, Warner-Bratzler shear force, drip loss and cooking loss. Meat and fat colour were measured using a Konica Minolta CR-400 Chromameter with a standard xenon lamp at 8 mm aperture. The experimental data was analysed using a mixed procedure in SAS, with diet included as a fixed effect and animal within diet as a random effect. Lamb was considered the experimental unit.

Results and discussion

Lamb performance

Lambs fed the Carrot TMR had a final live weight 1.7 kg greater than lambs on the Control TMR (40.5 vs 38.8 kg; P = 0.02). This indicates that the lambs fed carrots in their TMR demonstrated slightly better growth performance than lambs on the control TMR. Dry matter intake of lambs was 9.3% higher for lambs fed the Control TMR (951 vs. 870 g; P < 0.01). Further, lambs fed the Carrot TMR had 22% greater average daily gain than lambs fed the Control TMR (Figure 6; P < 0.01).

Carrot-fed lambs had better feed conversion efficiency, requiring 4.70 kg of feed (DM) for 1 kg of live weight gain compared to the 6.34 kg DM of the Control TMR per kg of live weight gain (i.e., required 26% less feed to achieve the same weight gain; Figure 7; P < 0.01). These results suggest that unsalable carrots are a suitable substitute for barley grain in lamb TMRs to improve production efficiency.

Figure 7 Feed conversion efficiency (g DM feed intake / g of liveweight gain) of lambs fed a control and carrot total mixed ration (*P<0.01)

Carcass traits

The improved production efficiency of lambs fed carrots in their TMR resulted in 1.7kg heavier hot and cold carcass weights following slaughter (P < 0.01) and an improved dressing percentage (P = 0.03). However, the diet did not influence the composition of the carcass, with no difference in muscling (eye muscle area) or fat depth between the TMR (Table 4; P ≥ 0.41).

 SEM: Standard error of mean

Meat quality

In line with our hypothesis, inclusion of unsalable carrots in the TMR did not influence meat quality parameters. The diet did not influence the ultimate pH of the carcass (P = 0.66; Table 5) and there was no difference in meat tenderness between the different TMRs as measured by Warner-Bratzler shear force (P = 0.77). Similarly, no difference was found in drip loss, cooking loss, meat colour or fat colour (P ≥ 0.08). 

SEM: Standard error of mean

Conclusion

The results of this study suggest that inclusion of unsalable carrots at up to 46% DM in a TMR can improve the efficiency of lamb meat production, without negatively influencing carcass and physical meat quality attributes.

The authors would like to thank Meat & Livestock Australia for their financial support of Daniel Forwood.