Green’s Dictionary of Slang

working bullock n.

In phrases

arse like a working bullock (also backside like...)

(N.Z.) having large buttocks.

[Aus]Canberra Times (ACT) 27 Dec. 6/3: You could hardly day she was a skinny girl. Matter of fact she had a backside on her like a working bullock.
[NZ] McGill Reed Dict. of N.Z. Sl. 26 Apr. [Internet] If you were laying on a beach [...] and some bugger came a wobbling along sporting an arse like a working bullock, you would stare.
like a working bullock (adj.)

1. (Aus.) used of unsuccessful racehorses, an image of ponderous sloth.

[Aus]Bell’s Life in Sydney 29 May 2/4: Circassian [a racehorse] laboured like a working bullock and The Hill was no better off.
[Aus]Sydney Mail 7 July 25/2: He ran like a working bullock in the A.J.C. Derby, but certainly retrieved his honour a little by running a good horse for the ‘Blue Ribbon’.
[Aus]Illus. Sydney News 15 Oct. 14/1: He finishes under the whip like a working bullock, and can have no possible chance of winning the Melbourne Cup.
[Aus]Sydney Sportsman (Surry Hills, NSW) 19 June 2/4: She, however, ran more like a working bullock than a racehorse.
Sydney Sportsman (Surry hills, NSW) 18 Jan. 8/2: Silver Head never once flattered his backers, and ran throughcut the race like a working bullock.
[Aus]Truth (Perth) 4 Aug. 7/4: ’Tis a funny thing, but nevertheless a fact, that whenever Peronne is backed and expected by one and sundry to win, he runs like a working bullock.
[Aus]Cumberland Argus (Parramatta, NSW) 7 Mar. 14/1: How are the might fallen. Theo, winner of two Derbies, ran like a working bullock in the V.R.C. St Leger on Saturday. Apparently he has lost all form.
Age (Melbvourne) 22 July 4/5: Ferguson said Warbird had galloped with Panax on Tuesday at Mentone, and had been beaten pointless. ‘In fact, he was going like a working bullock’.
Brisbane Teleg. (Qld) 15 Jan. 2/4: Holway also came sweeping down with long, powerful strides . . . but he was like a working bullock compared with the graceful action of Donaldson, ‘The Blue Streak’.

2. (Aus.) strong and dutiful if inelegant.

[Aus]Sydney Morn. Herald 5 Jan. 3/2: Mr Yaylor turned out of his bed between one and two in the morning and went down [...] to vote like a working bullock.
Longreach Leader (Qld) 14 Dec. 33/5: He was a big ex-policeman from Belfast and could pull like a working bullock.