Faecal testing confirms legume paddocks can improve heifer growth at the end of the NQ dry season

In a recent article, the NQPRP team described our experience measuring the feed quality of legume-grass pastures grazed by steers and heifers in some of our north Queensland demonstration sites. The legume pastures were providing a higher quality diet and increasing animal liveweight gain compared to native pastures. Read the article here. This involved stalking cattle grazing the pastures to sample fresh poo and getting it analysed using (Faecal) Near Infrared Reflectance Spectroscopy (FNIRS).  The results told us what the digestibility (using metabolisable energy as a proxy), crude protein and non-grass content of the diet was over the grazing period – all really useful information for understanding what the cattle are eating and how this is contributing to the liveweight gain we were measuring at the same time.

So, all fine, except that we had not finished the data collection for one of the sites where we were looking at diet quality during the critical late dry-season period and the onset of the wet season.  Here we provide the update, with a refresher on what we did at that particular site.

Key take-home messages

• Faecal sampling showed some important changes in diet composition and quality at the transition from the late dry to wet seasons
• Heifers grazing grass-legume pastures had a higher quality diet than adjacent unimproved pastures in the dry season, mostly due to the consumption of legumes
• The transition to the wet season saw the high quality grasses forming the basis of the diet in both paddocks
• Heifers in the grass-legume pasture gained 0.29 kg/hd/day between September and February, potentially improving the opportunity for early conception.
• The capacity to benefit from legume pastures requires making earlier grazing management decisions so there is a ‘stockpile’ of legume leaf available to improve the diet in the dry season.

Whitewater Station – fertile ground for research

The north Queensland sown pasture team have now been working for ten years with Tom and Christine Saunders at ‘Whitewater Station’ near Mount Surprise seeking legume options and pasture production systems which can improve the productivity and profitability of native grass pastures on fertile (very high phosphorous but low sulphur) red basalt soils.  The 6-ha paddock used for the demonstration originally contained about 0.3 ha of small plots established by broadcasting 1:1 combinations of well-adapted grasses (8) and legumes (8) into cultivated plots in February 2019.  These plots were wet season spelled and grazed in the dry season after measuring pasture yield and composition each year after establishment.  Two legumes, Caatinga stylo (Stylosanthes seabrana) and butterfly pea (Clitoria ternatea) had spread out of the plots and into the black speargrass (Heteropogon contortus) pasture which, like many of these grasslands in the region, have become dominated with the introduced grasses Indian couch (Bothriochloa pertusa) and grader grass (Themeda quadrivalvis). Once the small-plot experiment was finished, it was decided to look at the quality of the new grass-legume pasture at the end of the dry season and compare it with the neighbouring undeveloped paddock considered to be typical of local ‘breeder’ paddocks.

On 1st September 2024, six heifers averaging 227 kg/head were introduced to the legume paddock which had been spelled since being grazed at the end of the wet season.  There was sufficient soil moisture for growth of the deep-rooted legumes after mid-July rainfall, but grass growth had slowed and most grasses had seeded (and therefore lost feed quality).  The neighbouring large paddock had also recently been stocked with cows and calves.  Both groups had access to urea supplied by dosing of the water supply.  The team collected dung samples in both paddocks in September (one week after entry into the legume-grass paddock), November and mid-January, and submitted them for FNIRS analysis (Gcology Data Services Pty. Ltd.).  The heifers were reweighed on 29 January 2025 and the trial was wound up.  Rainfall was typical for the region, with the wet season not beginning until December when the monsoon trough delivered over 400 mm rainfall over the month.  This resulted in a rapid transition from dormant to vigorously growing grasses in both paddocks.  January was relatively dry, but soil moisture was sufficient to maintain vigorous grass growth by the end of the trial.

So, runs on the board?

The dung testing showed a clear difference in diet quality between the sown legume and undeveloped native grass pastures even though nitrogen was supplemented through the urea.  Dietary crude protein levels were relatively high at 7.3% (compared to 3.4% in the adjacent paddock) in the legume paddock when the cattle were introduced into the paddock.  These high crude protein levels coincided with high (>65%) levels of non-grass in the diet, indicating legume leaf represented a significant proportion of the diet (only 10% in the adjacent paddock).  The proportion of non-grass in the diet declined to <30% by November.  This is presumably because the cattle (stocked at high stocking rates) reduced (ate) the proportion of legume leaf available as they sought a high quality diet under dry conditions. This was associated in a decline in crude protein and metabolisable energy in the diet to levels similar to those of the adjacent native grass pasture.

The rainfall in December was associated with an increase in feed value to levels suitable for rapid animal growth as is typical in the northern summer.  Cattle used grass as the key feed source at this time.  However, dietary crude protein levels were slightly higher in the legume paddock, presumably due to the slightly higher proportion of ‘non-grass’ (presumably legume) in the diet.  The legumes in the sown pasture may have also benefitted grass production through improving the availability of nitrogen to grasses (and other plants), but this was not measured in this demonstration.

Result number two  – the heifers

The six heifers introduced on 1^st September averaged 0.29 kg/hd/day over the 151 days they were in the 6 ha paddock, gaining 43 kg/hd on average.  Individual growth rates ranged from 0.25 to 0.36 kg/hd/day.  These are excellent growth rates for this time of the year at a time when cattle lose weight grazing native grass pastures without supplementation (supplied as urea in drinking water in this case).  We were unable to weigh the cows and calves in the large native grass paddock, but infer that the higher quality diet in the grass-legume pasture likely resulted in better animal performance.

Something to ruminate over

With the completion of this second FNIRS trial of grass-legume pastures, we continue to see good relationships between the dung sample results, what is happening in the pasture and animal performance.  Such information can support visual cues for producers seeking to manage their grazing as the composition of the diet changes.  The excellent growth performance of the heifers when run at high stocking rates at the end of the dry season is exciting as it targets a problem period for cattle breeders in the area.  However, it should be remembered this was achieved on pasture in which legume leaf had been accumulated through spelling at the start of the dry season and December rainfall improved the amount and quality of grass available in the last Six weeks of the demonstration.  Nevertheless, Tom’s comment was that the performance was “quite exceptional” as it means there is a better opportunity to achieve early first conception in his heifers if such systems can be scaled up.

For information, get in touch with the NQ team.

This work is part of The Queensland Pasture Resilience Program, a partnership between the Department of Primary Industries, Meat & Livestock Australia, and the Australian Government through the MLA Donor Company.